Maintainer scripts for el file removal

[Jonathan Nieder <jrnieder@gmail.com>]

Hi,

Git commit 0944224a8d46 (git{,-blame}.el: remove old bitrotting Emacs
code, 2018-03-13, [1]) removes two elisp modules from Git that are
redundant next to modules available in other packages.  Good!  Now as
packager I would like to make the transition as smooth for users as I
can.

Git's emacs support is in a package named git-el ('fast, scalable,
distributed revision control system (emacs support)').  It provides
emacsen-common scripts to compile the elisp and a site-start script to
load it.

Questions:

 1. What should I put in maintainer scripts to be sure that the
    compiled elisp gets properly removed on upgrade?  Are there
    existing packages I can imitate for this?  Should I declare a
    Breaks by git against the old git-el package and rely on its
    existing scripts?

 2. Aside from updating the README.emacs in the Git package, is there
    anything I can do to make the transition more smooth for users?

 3. Any other words of advice?

Thanks,
Jonathan

[1] https://kernel.googlesource.com/pub/scm/git/git/+/0944224a8d4668c98e4eca0cbe67c4d0d88aa932%5E%21/