chore: remove unused import

Author: diegomarquezp

oauth2_http/java/com/google/auth/oauth2/ExternalAccountCredentials.java

@@ -37,7 +37,6 @@
 import com.google.api.client.json.GenericJson;
 import com.google.api.client.json.JsonObjectParser;
 import com.google.api.client.util.Data;
-import com.google.api.core.ObsoleteApi;
 import com.google.auth.RequestMetadataCallback;
 import com.google.auth.http.HttpTransportFactory;
 import com.google.common.base.MoreObjects;