subrepo: drop unused pattern initialization in hgsubrepo revert
This passed an empty list to filerevert() if '--all' was specified, otherwise
the set of modified files. But then filerevert() immediately switched this and
reinitialized 'pats' to an empty list if '--all' was *not* specified.
$ hg init
$ echo a > a
$ hg ci -qAm 'add a'
$ hg init subrepo
$ echo 'subrepo = http://example.net/libfoo' > .hgsub
$ hg ci -qAm 'added subrepo'
$ hg up -qC 0
$ echo ax > a
$ hg ci -m 'changed a'
created new head
$ hg up -qC 1
$ cd subrepo
$ echo b > b
$ hg add b
$ cd ..
Should fail, since there are added files to subrepo:
$ hg merge
abort: uncommitted changes in subrepository 'subrepo'
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