Update the flag check repohook to be same as go/android-flag-directive

* Flag type check, legacy or aconfig is removed. Legacy flags should use EXEMPT.
* Removed the flag status check.

Flags will be hyperlinked with gantry link and this will be supported by trunk stable team. See b/338407385 for details.

Error message when flag check fails : https://screenshot.googleplex.com/5bJ6k2KgUw3UTTG.png

Flag: NONE Repohook update
Test: Manual
Bug: 335029626

Change-Id: Ie4d12c33e867ee65f531be50c29c7ecf4455eda6