Remove unused it-gcp and it-jdbc modules

[Abacn]

Part of #30206

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[Abacn]

Besides the reasons in #30206 , for it-gcp itself, it was found in Beam 2.54.0rc1 validation that some changes need to be made in it-gcp component itself: https://github.com/GoogleCloudPlatform/DataflowTemplates/pull/1313/files#diff-ca10da4b6f0b454247e31d288a7c6492c0dcb1bb3c78eaab028f2c7716876802. If it-gcp were in Beam repo, it then had to trigger build another rc just for the fix of it-gcp module.

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