Delete all the usages of the flag and all the code that was executed when this flag was false.

https://linear.app/comm/issue/ENG-6415/deprecate-usingcommservicesaccesstoken

Depends on D14577

Flow. Tested with the rest of the stack:

1. Registered a new account on native
2. Wiped the state
3. Restored the account
4. Logged in on web
5. Checked that the app works by sending some messages in thick threads