Sema: Remove a call to setInvalid() that was messing up code completion results

setInvalid() sets the interface type of the declaration to ErrorType.

We should remove it eventually.

Author: slavapestov

Diff for: lib/Sema/TypeCheckProtocol.cpp

@@ -3376,8 +3376,6 @@ void ConformanceChecker::recordTypeWitness(AssociatedTypeDecl *assocType,
 
     aliasDecl->setImplicit();
     aliasDecl->setSynthesized();
-    if (type->hasError())
-      aliasDecl->setInvalid();
 
     // Inject the typealias into the nominal decl that conforms to the protocol.
     if (auto nominal = DC->getSelfNominalTypeDecl()) {