undo-files: also remove the undo.backupfiles
The undo.backupfiles is dealt is directly managed by the transaction instead of
going through the `localrepo.undofiles`. We start doing minimal management for
it before using `cleanup_undo_files` on more situation. Proper handling of it
is an intermediate goal of this series.
#require symlink
https://bz.mercurial-scm.org/1438
$ hg init repo
$ cd repo
$ ln -s foo link
$ hg add link
$ hg ci -mbad link
$ hg rm link
$ hg ci -mok
$ hg diff -g -r 0:1 > bad.patch
$ hg up 0
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg import --no-commit bad.patch
applying bad.patch
$ hg status
R link
? bad.patch