Use the Snap versioning automation of ubuntu/desktop-snaps (#20)

Remove the versioning automation scripting from snapcraft.yaml and add
the needed changes so that the GitHub action of ubuntu/desktop-snaps
does the versioning automation.

- Hard-code "version" and "grade" metadata fields in
  snapcraft.yaml. The GitHub action modifies this file to bump the
  version. This also improves readability, having the current version
  number visible near the top of the file.

- Remove the versioning automation scripting in the "override-pull:" in
  the "cups" part. We use the versioning automation in the GitHub
  action and do not need our own script any more.

- Remove the "jq" from the "build-packages:" in the "cups"
  part. This was only needed for our own versioning automation script.

- In the workflow file, .github/workflows/auto-update.yml, we add the
  parameter "version-schema: 'v(\d+\.\d+\.\d+)'" to the call
  of the GitHub action. This tells to the action to also perform
  versioning automation and it also tells the format of the upstream
  release tags and the upstream version number in them.

- We do not remove the "adopt-info: cups" even with all
  metadata fields in snapcraft.yaml being hard-coded and no "craftctl
  set ..." calls in the "cuos" part. It only tells the GitHub
  action which part is the supplier of the upstream version number.

.github/workflows/auto-update.yml

@@ -17,3 +17,4 @@ jobs:
         with:
           token: ${{ secrets.GITHUB_TOKEN }}
           repo: ${{ github.repository }}
+          version-schema: 'v(\d+\.\d+\.\d+)'

snapcraft.yaml

@@ -1,5 +1,7 @@
 name: cups
 base: core22 # The base Snap is the execution environment for this Snap
+version: '2.4.7-6'
+grade: stable
 summary: CUPS-based printing stack Snap
 description: Complete printing environment in a Snap
 confinement: strict
@@ -196,62 +198,6 @@ parts:
       # Do the actual pull task
       craftctl default
       # Settings:
-      # Force channel: auto/devel/edge/stable
-      CHANNEL=stable
-      # Force package release number (integer) or "auto"
-      PACKAGERELEASE=auto
-      # Time stamp of Snap build in Snap Store
-      snapbuilddatehuman=`curl -s -H 'Snap-Device-Series: 16' https://api.snapcraft.io/v2/snaps/info/cups | jq -r '."channel-map" | .[] | select(.channel.name == "edge") | select(.channel.architecture == "amd64") | ."created-at"'`
-      snapbuilddate=`date +%s --date=$snapbuilddatehuman`
-      if [ -z "$snapbuilddate" ]; then
-          snapbuilddate=0
-      fi
-      # Time stamp of the last GIT commit of the snapping repository
-      pushd $CRAFT_PROJECT_DIR
-      gitcommitdate=`git log -1 --date=unix | grep Date: | perl -p -e 's/Date:\s*//'`
-      popd
-      if [ -z "$gitcommitdate" ]; then
-          gitcommitdate=0
-      fi
-      # Previous stable and development version
-      prevstable="$(curl -s -H 'Snap-Device-Series: 16' https://api.snapcraft.io/v2/snaps/info/cups | jq -r '."channel-map" | .[] | select(.channel.name == "stable") | select(.channel.architecture == "'$CRAFT_TARGET_ARCH'") | .version')"
-      if [ -z "$prevstable" ]; then
-          prevstable=0
-      fi
-      prevdevel="$(curl -s -H 'Snap-Device-Series: 16' https://api.snapcraft.io/v2/snaps/info/cups | jq -r '."channel-map" | .[] | select(.channel.name == "edge") | select(.channel.architecture == "'$CRAFT_TARGET_ARCH'") | .version')"
-      if [ -z "$prevdevel" ]; then
-          prevdevel=0
-      fi
-      # Previous version in general
-      dpkg --compare-versions "$prevdevel" lt "$prevstable" && prevversion=$prevstable || prevversion=$prevdevel
-      # Current upstream version of CUPS
-      upstreamversion="$(git describe --tags --always | sed -e 's/^v//;s/-/+git/;y/-/./')"
-      # Determine package release number
-      if test "x$PACKAGERELEASE" = "xauto"; then
-          packagerelease=`echo "$prevversion" | perl -p -e 's/^('"$upstreamversion"'\-(\d+)|.*)$/\2/'`
-          if [ -z "$packagerelease" ]; then
-              packagerelease=1
-          else
-              if test "$gitcommitdate" -gt "$snapbuilddate"; then
-                  packagerelease=$(( $packagerelease + 1 ))
-              fi
-          fi
-      else
-          packagerelease=$PACKAGERELEASE
-      fi
-      # Compose version string
-      version="$upstreamversion-$packagerelease"
-      # Select channel
-      if test "x$CHANNEL" = "xedge" -o "x$CHANNEL" = "xdevel"; then
-          grade=devel
-      elif test "x$CHANNEL" = "xstable"; then
-          grade=stable
-      else
-          [ -n "$(echo $version | grep "+git")" ] && grade=devel || grade=stable
-      fi
-      # Set version and grade
-      craftctl set version="$version"
-      craftctl set grade="$grade"
       # Patch to use snapctl with the slot name "cups-server" for Snap mediation
       #patch -p1 < $CRAFT_PROJECT_DIR/patches/use-snapctl-with-slot-cups-server.patch
       # Longer timeout for Avahi resolving for cupsGetDests() API function, used
@@ -261,7 +207,6 @@ parts:
       - git
       - sed
       - curl
-      - jq
       - perl-base
       - patch
       - autoconf