Deprecate the latest branch in go SDK repo (#10372)

Author: ArcturusZhang

specificationRepositoryConfiguration.json

@@ -3,7 +3,6 @@
   "pipelineName": "automation - sdk",
   "sdkRepositoryMappings": {
     "azure-sdk-for-go": {
-      "mainBranch": "latest",
       "integrationRepository": "AzureSDKAutomation/azure-sdk-for-go",
       "mainRepository": "Azure/azure-sdk-for-go"
     },