Remove grenade-skip-level job from non SLURP master

Current master branch (2024.2) is non SLURP release and
grenade-skip-level job is not supposed to run on non SLURP
gate.If any project want to test upgrade from stable/2023.2
to 2024.2 then they can use grenade-skip-level-always job.

Keeping its job definition create more issue and confusion when
zuul looks for the job selection.

Change-Id: I705996a9eefd40b975080cdc51b68c4467b94437

.zuul.yaml

@@ -9,14 +9,14 @@
         - octavia-grenade
         - ironic-grenade:
             voting: false
-        - grenade-skip-level
+        - grenade-skip-level-always
     gate:
       jobs:
         - grenade
         - grenade-multinode
         - grenade-heat-multinode
         - octavia-grenade
-        - grenade-skip-level
+        - grenade-skip-level-always
     experimental:
       jobs:
         - grenade-postgresql
@@ -396,24 +396,3 @@
       grenade_from_branch: stable/2023.1
       grenade_localrc:
         NOVA_ENABLE_UPGRADE_WORKAROUND: True
-
-- job:
-    name: grenade-skip-level
-    description: |
-      Grenade job that skips a release, validating that deployers can skip
-      specific releases as prescribed by our process.
-    nodeset: openstack-single-node-jammy
-    parent: grenade-skip-level-always
-      # NOTE(gmann): This job is meant to validate the SLURP to SLURP release
-      # upgrade so it supposed to run on SLURP release gate only. If current master
-      # is not SLURP release,we can remove the job definition from master branch.
-      # SLURP release upgrade jobs are defined in their respective stable branch.
-      # If you would like to run N-2 -> N upgrade testing on non SLURP releases
-      # then use grenade-skip-level-always job.
-      # Along with grenade gate, this job runs on many other projects gate
-      # also and in this job definition, we control for everyone to run on SLURP
-      # release only.
-    vars:
-      grenade_from_branch: stable/2023.1
-    branches:
-      - master