fix: Remove unnecessary import in client_test.dart

BadRequest is already exported from grpc.dart, so the separate import
of error_details.pb.dart is unnecessary.

Author: tsavo-at-pieces

test/client_tests/client_test.dart

@@ -19,8 +19,7 @@ import 'dart:io' show HttpStatus;
 
 import 'package:grpc/grpc.dart';
 import 'package:grpc/src/client/http2_connection.dart';
-import 'package:grpc/src/generated/google/rpc/error_details.pb.dart'
-    show BadRequest;
+// BadRequest is exported from grpc.dart, no need for separate import
 import 'package:grpc/src/generated/google/rpc/status.pb.dart';
 import 'package:grpc/src/shared/status.dart';
 import 'package:http2/transport.dart';