[NFC] Remove an unused local variable in isolated parameter checking.

(cherry picked from commit 4ff4cfd)

Author: hborla

lib/Sema/TypeCheckConcurrency.cpp

@@ -3469,17 +3469,6 @@ namespace {
         if (getIsolatedActor(arg) || isa<CurrentContextIsolationExpr>(arg))
           continue;
 
-        // An isolated parameter was provided with a non-isolated argument.
-        // FIXME: The modeling of unsatisfiedIsolation is not great here.
-        // We'd be better off using something more like closure isolation
-        // that can talk about specific parameters.
-        auto nominal = getType(arg)->getAnyNominal();
-        if (!nominal) {
-          // FIXME: This is wrong for distributed actors.
-          nominal = getType(arg)->getASTContext().getProtocol(
-              KnownProtocolKind::Actor);
-        }
-
         auto calleeIsolation = ActorIsolation::forActorInstanceParameter(
             const_cast<Expr *>(arg->findOriginalValue()), paramIdx);