build: --credential-file-override is no longer required (#391)

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Source-Link: googleapis/synthtool@94421c4

packages/google-cloud-bigquery-datatransfer/synth.metadata

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/nodejs-bigquery-data-transfer.git",
-        "sha": "b2d38fa4edf785a6bfcc766bf1fb61d62693cba4"
+        "sha": "2e430a39b438ecfe60d7793ecfbedfe782b5e468"
       }
     },
     {
@@ -19,7 +19,7 @@
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "5936421202fb53ed4641bcb824017dd393a3dbcc"
+        "sha": "94421c47802f56a44c320257b2b4c190dc7d6b68"
       }
     }
   ],