[NFC] Remove Unused Module Parameter to Conformance Lookup

It's been quite a long time since this unused parameter was introduced.
The intent is to produce the module as a root for the search - that is,
computing the set of conformances visible from that module, not the set
of conformances inside of that module. Callers have since been providing
all manner of module-scoped contexts to it.

Let's just get rid of it. When we want to teach protocol conformance
lookup to do this, we can revert this commit as a starting point and try
again.

lib/Frontend/ModuleInterfaceSupport.cpp

@@ -502,7 +502,7 @@ public:
                                           const NominalTypeDecl *nominal,
                                           ProtocolDecl *proto) {
     SmallVector<ProtocolConformance *, 4> conformances;
-    nominal->lookupConformance(M, proto, conformances);
+    nominal->lookupConformance(proto, conformances);
     return llvm::all_of(conformances,
                         [M](const ProtocolConformance *conformance) -> bool {
       return M == conformance->getDeclContext()->getParentModule();