Remove unused type parameter

This CL removes an unused type parameter from a test in _macros.
The type parameter gave rise to a warning from the lint
`avoid_types_as_parameter_names` because it had the same name as a
type in scope (`Declaration`).

The type variable could also have been renamed, but it seems very unlikely that any other part of the system will break because the type parameter has been removed: The function is declared in a test, and nothing in the test depends on that type parameter in any way.

See also dart-lang/linter#5066 for details.

Change-Id: Ibc42c4a758f70564c9fe12f3bf2bfbb72e63e97d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/383600
Reviewed-by: Jake Macdonald <[email protected]>

pkg/_macros/test/executor/serialization_test.dart

@@ -765,7 +765,7 @@ void expectSerializationEquality<T extends Serializable>(T serializable,
 
 /// Deserializes [serialized] in its own remote instance cache and sends it
 /// back.
-Object? roundTrip<Declaration>(Object? serialized, int zoneId) {
+Object? roundTrip(Object? serialized, int zoneId) {
   return withRemoteInstanceZone(zoneId, () {
     var deserializer = deserializerFactory(serialized);
     var instance = RemoteInstance.deserialize(deserializer) as Serializable;