NCGenerics: remove optimistic assertion

I thought it might be impossible to recursively lookupConformance of
Copyable, unlike for Sendable. Turns out there are still situations
where it can happen, that aren't invalid.

This alone fixes `ClangImporter/objc_bridging_generics.swift` and will
help reveal any invalid request cycles.

Author: kavon

lib/AST/ConformanceLookup.cpp

@@ -178,7 +178,6 @@ ProtocolConformanceRef ModuleDecl::lookupConformance(Type type,
       ImplicitKnownProtocolConformanceRequest icvRequest{nominal, *kp};
       if (getASTContext().evaluator.hasActiveRequest(icvRequest) ||
           getASTContext().evaluator.hasActiveRequest(request)) {
-        assert(!getInvertibleProtocolKind(*kp));
         return ProtocolConformanceRef::forInvalid();
       }
     }