oauth2/google: remove meta validations for aws external credentials

Remove the url validations to keep a consistency with other libraries.

Change-Id: Icb1767edc000d9695db3f0c7ca271918fb2083f5
GitHub-Last-Rev: af89ee0c72
GitHub-Pull-Request: golang/oauth2#660
Reviewed-on: https://go-review.googlesource.com/c/oauth2/+/522395
Reviewed-by: Leo Siracusa <leosiracusa@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cody Oss <codyoss@google.com>
Run-TryBot: Cody Oss <codyoss@google.com>

google/internal/externalaccount/basecredentials.go

@@ -185,10 +185,6 @@ func (c *Config) parse(ctx context.Context) (baseCredentialSource, error) {
 				awsCredSource.IMDSv2SessionTokenURL = c.CredentialSource.IMDSv2SessionTokenURL
 			}
 
-			if err := awsCredSource.validateMetadataServers(); err != nil {
-				return nil, err
-			}
-
 			return awsCredSource, nil
 		}
 	} else if c.CredentialSource.File != "" {