Remove `github`, `gitlab`, `bitbucket`, `gitea` fields in the commit context

[MarcoIeni]

Is there an existing issue or pull request for this?

• [X] I have searched the existing issues and pull requests

Feature description

https://github.com/orhun/git-cliff/pull/822 added the remote field and deprecated these fields. We want to remove them to optimize memory usage, as requested in https://github.com/orhun/git-cliff/pull/822#pullrequestreview-2305451241

Desired solution

These fields don't exist anymore

Alternatives considered

keep these fields for retrocompatibility

Additional context

should we release git-cliff 3 after this change? Or we are allowed to change this part of the changelog because it's considered "experimental"?

[orhun]

should we release git-cliff 3 after this change? Or we are allowed to change this part of the changelog because it's considered "experimental"?

Probably not, and yes, should be fine :)