lint fixes.

Author: vverman

google-auth-library-java/oauth2_http/java/com/google/auth/oauth2/GoogleCredentials.java

@@ -39,7 +39,6 @@
 import com.google.auth.RequestMetadataCallback;
 import com.google.auth.http.AuthHttpConstants;
 import com.google.auth.http.HttpTransportFactory;
-import com.google.auth.mtls.MtlsUtils;
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.MoreObjects;
 import com.google.common.base.MoreObjects.ToStringHelper;