[REM] codeowner: remove github codeowner

Github codeowner is replaced with a runbot version of codeowners for
multiple reason:

- github codeowners is difficult to maintain, the precedence rule will
sometimes remove teams from some file because of a more specific rule
added by another team.

- github codeowner does not support version specific rules, especially
the "all except master" rule. For this use case teams needs to adapt
the new codeowner when freezing a new version.

- github will trigger codeowner on failed rebase, and add almost all
teams as reviewer. Runbot has specific commit and file limit to avoid
this problem.

- runbot codeowner is centralised and does not need to be managed cross
repo/version

- runbot codeowner works for enterprise

Any mofification on codeowner should be requested to runbot team.

closes odoo#74127

X-original-commit: 305a42f
Signed-off-by: Xavier Dollé (xdo) <[email protected]>

Author: Xavier-Do