Remove support for release notes in create tag API
It was deprecated in 11.7, so we should finally remove it:
- https://gitlab.com/gitlab-org/gitlab/blob/ea5c474169b13278b21efc285e097b63cf831454/lib/api/tags.rb#L65
- https://gitlab.com/gitlab-org/gitlab/blob/ea5c474169b13278b21efc285e097b63cf831454/lib/api/tags.rb#L108
- https://gitlab.com/gitlab-org/gitlab/blob/ea5c474169b13278b21efc285e097b63cf831454/lib/api/tags.rb#L140