[Serialization] Remove treatAsPartialModule parameter

This information can be derived from whether we're
installing the module file into the main module.

tools/SourceKit/lib/SwiftLang/SwiftIndexing.cpp

@@ -186,8 +186,7 @@ static void indexModule(llvm::MemoryBuffer *Input,
     // correct filename here.
     auto FUnit = Loader->loadAST(*Mod, None, /*moduleInterfacePath*/"",
                                  std::move(Buf), nullptr, nullptr,
-                                 /*isFramework*/false,
-                                 /*treatAsPartialModule*/false);
+                                 /*isFramework*/false);
 
     // FIXME: Not knowing what went wrong is pretty bad. loadModule() should be
     // more modular, rather than emitting diagnostics itself.