Delete ./vendor before each sync

This workarounds missing namespace errors (see #
674)

src/new_build.sh

@@ -27,6 +27,7 @@
 #      -  RETRY_FETCHES
 # - Branch-specific stuff
 # - handle local manifests
+# - Delete ./vendor
 # - Sync mirror if we're using one
 # -  main sync and build loop
 #    For each device in `$DEVICE_LIST`
@@ -169,6 +170,9 @@ if [ "$INCLUDE_PROPRIETARY" = true ]; then
     "https://gitlab.com/the-muppets/manifest/raw/$themuppets_branch/muppets.xml" .repo/local_manifests/proprietary_gitlab.xml
 fi
 
+# Delete ./vendor
+rm -rf vendor || true
+
 # Sync mirror if we're using one
 if [ "$LOCAL_MIRROR" = true ]; then