[CS] Remove external type logic from getTypeForPattern

This shouldn't be necessary, we should be able to
solve with type variables instead. This makes sure
we don't end up with weird special cases that only
occur when an external type is present.

lib/Sema/CSDiagnostics.cpp

@@ -8756,7 +8756,7 @@ bool InvalidWeakAttributeUse::diagnoseAsError() {
     return false;
 
   auto *var = pattern->getDecl();
-  auto varType = OptionalType::get(getType(var));
+  auto varType = getType(var);
 
   auto diagnostic =
       emitDiagnosticAt(var, diag::invalid_ownership_not_optional,