repoupdater: Remove p4 binary from docker image (#57120)

After https://github.com/sourcegraph/sourcegraph/pull/57119, we no longer need the p4 binary to be present in repo-updater, so we can remove it.
Less headache when moving around processes when figuring out if p4 code is actually working in the container :)

cmd/repo-updater/image_test.yaml

@@ -6,10 +6,6 @@ commandTests:
     envVars:
       - key: "SANITY_CHECK"
         value: "true"
-  - name: "p4 is runnable"
-    command: "p4"
-    args:
-      - -h
   - name: "coursier is runnable"
     command: "coursier"
 

wolfi-images/repo-updater.yaml

@@ -8,6 +8,5 @@ contents:
 
     ## repo-updater packages
     - coursier@sourcegraph
-    - p4cli@sourcegraph
 
 # MANUAL REBUILD: Fri 29 Sep 2023 11:16:10 EDT