[TASK] Remove repository polling trigger from pre-merge test plans

The trigger will cause the plan to be executed after merge, which
is not needed because nightly plans take care of it.

Resolves: #89972
Releases: master, 9.5, 8.7
Change-Id: Iafc32174d2234439915c2e741020c4626391f98a
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/62767
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>

Build/bamboo/src/main/java/core/PreMergeSpec.java

@@ -66,10 +66,7 @@ Plan createPlan() {
                 stageMainStage
             )
             .linkedRepositories("github TYPO3 TYPO3.CMS 9.5")
-            .triggers(
-                new RepositoryPollingTrigger()
-                    .name("Repository polling for post-merge builds"),
-                getGerritTrigger())
+            .triggers(getGerritTrigger())
             .variables(
                 new Variable("changeUrl", ""),
                 new Variable("patchset", "")