simplemerge: move default labels to simplemerge extension
I want to remove knowledge of paths from the `simplemerge` core
module. As part of that, let's move the default labels from the core
module to the extension.
Differential Revision: https://phab.mercurial-scm.org/D11977
#require clang-format test-repo
$ . "$TESTDIR/helpers-testrepo.sh"
$ cd "$TESTDIR"/..
$ for f in `testrepohg files 'set:(**.c or **.cc or **.h) and not "listfile:contrib/clang-format-ignorelist"'` ; do
> clang-format --style file $f > $f.formatted
> cmp $f $f.formatted || diff -u $f $f.formatted
> rm $f.formatted
> done