transaction: rename find to findoffset and drop backup file support
transaction.find used to support access to both the regular file and
backup file list. They have different formats, so any consumer has to be
aware of the difference alredy. There is no in-core consumer for the
backup file access, so don't provide it.
Differential Revision: https://phab.mercurial-scm.org/D9276
#require emacs
$ emacs -q -no-site-file -batch -l $TESTDIR/../contrib/hg-test-mode.el \
> -f ert-run-tests-batch-and-exit
Running 1 tests (*) (glob)
passed 1/1 hg-test-mode--compilation-mode-support* (glob)
Ran 1 tests, 1 results as expected* (glob)