build: --credential-file-override is no longer required (#371)

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Source-Link: googleapis/synthtool@94421c4

packages/google-cloud-kms/synth.metadata

@@ -4,7 +4,7 @@
  "git": {
  "name": ".",
  "remote": "https://github.com/googleapis/nodejs-kms.git",
- "sha": "07a6437221179c9e135a55e68cff48f08b490f66"
+ "sha": "df35fe7c4186f903923660de868d71174d22d94c"
  }
  },
  {
@@ -19,7 +19,7 @@
  "git": {
  "name": "synthtool",
  "remote": "https://github.com/googleapis/synthtool.git",
- "sha": "5936421202fb53ed4641bcb824017dd393a3dbcc"
+ "sha": "94421c47802f56a44c320257b2b4c190dc7d6b68"
  }
  }
  ],