chore: manage hermetic_library_generation action version via Hermetic Build only (#3170)

The fix googleapis/sdk-platform-java#3800 was meant for GraalVM image versions.
The regression in #3169, however, affects the hermetic_library_generation GH action instead, which is not in the sdk-platform-java template, but java-storage does not consume the renovate.json template as per its owlbot.py.

Author: diegomarquezp

renovate.json

@@ -20,16 +20,6 @@
       "matchStrings": ["uses: googleapis/sdk-platform-java/java-shared-dependencies/unmanaged-dependency-check@google-cloud-shared-dependencies/v(?<currentValue>.+?)\\n"],
       "depNameTemplate": "com.google.cloud:sdk-platform-java-config",
       "datasourceTemplate": "maven"
-    },
-    {
-      "fileMatch": [
-        ".github/workflows/hermetic_library_generation.yaml"
-      ],
-      "matchStrings": [
-        "uses: googleapis/sdk-platform-java/.github/scripts@v(?<currentValue>.+?)\\n"
-      ],
-      "depNameTemplate": "com.google.api:gapic-generator-java",
-      "datasourceTemplate": "maven"
     }
   ],
   "packageRules": [