Update MergeRequest API state_event option documentation
What
Removing merge from MergeRequest API #update documentation.
Also fixes some changes from https://gitlab.com/gitlab-org/gitlab-ce/commit/8b5c16e4b1d54745ba6ca65ecfbf14c1683db3b4
Why
Merge option has long since been moved to a separate endpoint.
Acceptance criteria?
-
Branch has no merge conflicts with master(if it does - rebase it please) -
Squashed related commits together