Bug 1218315 - Use L"..." instead of MOZ_UTF16(...) for MSVS2015. r=nfroyd

xpcom/base/nsSystemInfo.cpp

@@ -191,7 +191,7 @@ nsresult GetInstallYear(uint32_t& aYear)
   time_t raw_time = 0;
   DWORD time_size = sizeof(time_t);
 
-  status = RegQueryValueExW(hKey, MOZ_UTF16("InstallDate"),
+  status = RegQueryValueExW(hKey, L"InstallDate",
                             nullptr, &type, (LPBYTE)&raw_time, &time_size);
 
   if (status != ERROR_SUCCESS) {