[Concurrency] Remove some dead code from mayExecuteConcurrentlyWith.

This code is no longer used given that region isolation is always enabled
along with strict concurrency checking.

(cherry picked from commit c283ce1)

Author: hborla

lib/Sema/TypeCheckConcurrency.cpp

@@ -4839,8 +4839,6 @@ bool ActorIsolationChecker::mayExecuteConcurrentlyWith(
   if (useContext == defContext)
     return false;
 
-  bool isolatedStateMayEscape = false;
-
   auto useIsolation = getActorIsolationOfContext(
       const_cast<DeclContext *>(useContext), getClosureActorIsolation);
   if (useIsolation.isActorIsolated()) {
@@ -4858,16 +4856,6 @@ bool ActorIsolationChecker::mayExecuteConcurrentlyWith(
     if (ctx.LangOpts.hasFeature(Feature::GlobalActorIsolatedTypesUsability) &&
         regionIsolationEnabled && useIsolation.isGlobalActor())
       return false;
-
-    // If the local function is not Sendable, its isolation differs
-    // from that of the context, and both contexts are actor isolated,
-    // then capturing non-Sendable values allows the closure to stash
-    // those values into actor isolated state. The original context
-    // may also stash those values into isolated state, enabling concurrent
-    // access later on.
-    isolatedStateMayEscape =
-        (!regionIsolationEnabled &&
-        useIsolation.isActorIsolated() && defIsolation.isActorIsolated());
   }
 
   // Walk the context chain from the use to the definition.
@@ -4877,18 +4865,13 @@ bool ActorIsolationChecker::mayExecuteConcurrentlyWith(
       if (closure->isSendable())
         return true;
 
-      if (isolatedStateMayEscape)
-        return true;
     }
 
     if (auto func = dyn_cast<FuncDecl>(useContext)) {
       if (func->isLocalCapture()) {
         // If the function is @Sendable... it can be run concurrently.
         if (func->isSendable())
           return true;
-
-        if (isolatedStateMayEscape)
-          return true;
       }
     }