Update BRANCH_SYSTEM.md

Removed step 3 in "beta on existing image"-block, because `G_DEV_BRANCH()` does a `/boot/dietpi/dietpi-update -1` anyway.

BRANCH_SYSTEM.md

@@ -16,9 +16,8 @@ By joining the Beta and reporting issues, you will be assisting DietPi (and all
     ```sh
     G_DEV_BRANCH beta
     ```
-3. Run `dietpi-update` to update the system, then reboot (or update quickly with `dietpi-update 1`).
-4. Test away, please report any issues on our GitHub page. Also ensure you mention "beta branch" in your post: https://github.com/MichaIng/DietPi/issues
-5. If you want to return the system to the previous restore state, run `dietpi-backup` to restore (or restore quickly with `dietpi-backup -1`).
+3. Test away, please report any issues on our GitHub page. Also ensure you mention "beta branch" in your post: https://github.com/MichaIng/DietPi/issues
+4. If you want to return the system to the previous restore state, run `dietpi-backup` to restore (or restore quickly with `dietpi-backup -1`).
 
 ## Steps to use the DietPi "dev" branch
 #### This is the active development branch. It is potentially unstable, unsupported and should not be used by end users.