[ModuleLoader] Remove forwarding module from CAS loader

For caching build that uses CAS module loader, it will never create
forwarding module, but references original binary module directoy.
Remove dead code. NFC.

Author: cachemeifyoucan

lib/Frontend/ModuleInterfaceLoader.cpp

@@ -2687,41 +2687,6 @@ bool ExplicitCASModuleLoader::findModule(
     return false;
   }
 
-  const bool isForwardingModule =
-      !serialization::isSerializedAST(moduleBuf->getBuffer());
-  // If the module is a forwarding module, read the actual content from the path
-  // encoded in the forwarding module as the actual module content.
-  if (isForwardingModule) {
-    auto forwardingModule = ForwardingModule::load(*moduleBuf.get());
-    if (forwardingModule) {
-      // Look through ExplicitModuleMap for paths.
-      // TODO: need to have dependency scanner reports forwarded module as
-      // dependency for this compilation and ingested into CAS.
-      auto moduleOrErr = Impl.loadModuleFromPath(
-          forwardingModule->underlyingModulePath, Ctx.Diags);
-      if (!moduleOrErr) {
-        llvm::consumeError(moduleOrErr.takeError());
-        Ctx.Diags.diagnose(SourceLoc(),
-                           diag::error_opening_explicit_module_file,
-                           moduleInfo.modulePath);
-        return false;
-      }
-      moduleBuf = std::move(*moduleOrErr);
-      if (!moduleBuf) {
-        // We cannot read the module content, diagnose.
-        Ctx.Diags.diagnose(SourceLoc(),
-                           diag::error_opening_explicit_module_file,
-                           moduleInfo.modulePath);
-        return false;
-      }
-    } else {
-      // We cannot read the module content, diagnose.
-      Ctx.Diags.diagnose(SourceLoc(), diag::error_opening_explicit_module_file,
-                         moduleInfo.modulePath);
-      return false;
-    }
-  }
-  assert(moduleBuf);
   // Move the opened module buffer to the caller.
   *ModuleBuffer = std::move(moduleBuf);