Fixes for the 5.5 branch

Author: DougGregor

lib/Sema/TypeCheckConcurrency.cpp

@@ -3010,7 +3010,6 @@ static bool checkClassGlobalActorIsolation(
     break;
 
   case ActorIsolation::ActorInstance:
-  case ActorIsolation::DistributedActorInstance:
     // This is an error that will be diagnosed later. Ignore it here.
     return false;
 
@@ -3577,7 +3576,6 @@ bool swift::checkSendableConformance(
   switch (getActorIsolation(nominal)) {
   case ActorIsolation::Unspecified:
   case ActorIsolation::ActorInstance:
-  case ActorIsolation::DistributedActorInstance:
   case ActorIsolation::Independent:
     break;