copies-rust: make more use of the new comparison property
We deal with the "both are the same" sooner and simplify the rest of the
conditional.
Differential Revision: https://phab.mercurial-scm.org/D9654
%include map-cmdline.default
[templates]
changeset = '{cset}{branches}{bookmarks}{tags}{lphase}{parents}{luser}{ldate}{summary}\n'
changeset_verbose = '{cset}{branches}{bookmarks}{tags}{lphase}{parents}{luser}{ldate}{lfiles}{lfile_copies_switch}{description}\n'