docs: Remove the separate commit document

It's part of the contribution guide.

README.commits

@@ -1,72 +0,0 @@
-GTK+ is part of the GNOME git repository. At the current time, any
-person with write access to the GNOME repository, can make changes to
-GTK+. This is a good thing, in that it encourages many people to work
-on GTK+, and progress can be made quickly. However, GTK+ is a fairly
-large and complicated package that many other things depend on, so to
-avoid unnecessary breakage, and to take advantage of the knowledge
-about GTK+ that has been built up over the years, we'd like to ask
-people committing to GTK+ to follow a few rules:
-
-0) Ask first. If your changes are major, or could possibly break existing
-   code, you should always ask. If your change is minor and you've
-   been working on GTK+ for a while it probably isn't necessary
-   to ask. But when in doubt, ask. Even if your change is correct,
-   somebody may know a better way to do things.
-
-   If you are making changes to GTK+, you should be subscribed
-   to gtk-devel-list@gnome.org. (Subscription address:
-   gtk-devel-list-request@gnome.org.) This is a good place to ask
-   about intended changes.
-
-   #gtk+ on GIMPNet (irc.gimp.org, irc.us.gimp.org, irc.eu.gimp.org, ...)
-   is also a good place to find GTK+ developers to discuss changes with,
-   however, email to gtk-devel-list is the most certain and preferred
-   method.
-
-1) Ask _first_.
-
-2) With git, we no longer maintain a ChangeLog file, but you are expected
-   to produce a meaningful commit message. Changes without a sufficient
-   commit message will be reverted. See below for the expected format
-   of commit messages.
-
-Notes:
-
-* When developing larger features or complicated bug fixes, it is
-  advisable to work in a branch in your own cloned GTK+ repository.
-  You may even consider making your repository publically available
-  so that others can easily test and review your changes.
-
-* The expected format for git commit messages is as follows:
-
-=== begin example commit ===
-Short explanation of the commit
-
-Longer explanation explaining exactly what's changed, whether any
-external or private interfaces changed, what bugs were fixed (with bug
-tracker reference if applicable) and so forth. Be concise but not too brief.
-=== end example commit ===
-
-  - Always add a brief description of the commit to the _first_ line of
-    the commit and terminate by two newlines (it will work without the
-    second newline, but that is not nice for the interfaces).
-
-  - First line (the brief description) must only be one sentence and
-    should start with a capital letter unless it starts with a lowercase
-    symbol or identifier. Don't use a trailing period either. Don't exceed
-    72 characters.
-
-  - The main description (the body) is normal prose and should use normal
-    punctuation and capital letters where appropriate. Normally, for patches
-    sent to a mailing list it's copied from there.
-
-  - When committing code on behalf of others use the --author option, e.g.
-    git commit -a --author "Joe Coder <joe@coder.org>" and --signoff.
-
-
-Owen Taylor
-13 Aug 1998
-17 Apr 2001
-
-Matthias Clasen
-31 Mar 2009