Remove old assertion about when we're allowed to use fileExists

Author: Andy Hanson

src/services/services.ts

@@ -3114,7 +3114,6 @@ namespace ts {
                 getCurrentDirectory: () => currentDirectory,
                 fileExists: (fileName): boolean => {
                     // stub missing host functionality
-                    Debug.assert(!host.resolveModuleNames || !host.resolveTypeReferenceDirectives);
                     return hostCache.getOrCreateEntry(fileName) !== undefined;
                 },
                 readFile: (fileName): string => {