Merge branch 'jp-remove-chat-flag' into 'master'

Remove ai_chat_history_context feature flag

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/130396



Merged-by: Alexandru Croitor <acroitor@gitlab.com>
Approved-by: Gosia Ksionek <mksionek@gitlab.com>
Approved-by: Alexandru Croitor <acroitor@gitlab.com>
Approved-by: Vitaly Slobodin <vslobodin@gitlab.com>
Co-authored-by: Jan Provaznik <jprovaznik@gitlab.com>