bug#6134: `make distclean' doesn't remove .elc files

[Paul Pogonyshev]

When I invoke

    make distclean

in a repository clone, I expect to get a completely clean tree, so
that next recompilation doesn't use any leftovers of previous one.
However, .elc files are not deleted and it is easy to forget that you
have to delete them manually if you are not recompiling Emacs on a
daily basis.

This, in particular, led to a "bug" report:

    http://debbugs.gnu.org/cgi/bugreport.cgi?bug=6107

Paul