github: workflows: emove zmain build test

This just adds more noise than signal to the CI results.

Signed-off-by: Liam Girdwood <liam.r.girdwood@linux.intel.com>

Author: lrgirdwo

.github/workflows/zephyr.yml

@@ -113,7 +113,6 @@ jobs:
         # Search "zephyr_revision" and see below what they expand to.
         zephyr_revision: [
           mnfst,  # special value: don't override sof/west.yml
-          zmain,  # Zephyr's main branch
         ]
         # Using groups to avoid spamming the small results box with too
         # many lines. Pay attention to COMMAS.
@@ -167,15 +166,7 @@ jobs:
           if [ 'mnfst' =  '${{ matrix.zephyr_revision }}' ]; then
              rem_rev=$(git -C zephyr rev-parse HEAD)
           else
-             case '${{ matrix.zephyr_revision }}' in
-               'zmain') rem_rev='main' ;;
-               *)       echo 'Unknown matrix.zephyr_revision'; exit 1 ;;
-             esac
-             ( cd sof/submanifests/
-               sed -e "s#=sof_zephyr_revision_override=#${rem_rev}#" \
-                 sof-ci-jenkins/zephyr-override-template.yml > test-zephyr-main.yml
-             )
-             time west update --narrow  --fetch-opt=--filter=tree:0
+             echo 'Unknown matrix.zephyr_revision'; exit 1
           fi
 
       # Get some tags to fix `git describe` hence BUILD_VERSION, etc.