histedit: remove an unnecessary default value of `b''` for commit message
I don't think `ctx.description()` is ever anything falsy other than
`b''`. I think the comment added in 4c4232e51167 (histedit: extract
common summary code into method, 2016-05-27) is mistaken (I don't see
any code following that pattern before the function was added).
Differential Revision: https://phab.mercurial-scm.org/D12406
$ hg init
$ echo a > a
$ hg ci -Ama
adding a
$ hg an a
0: a
$ hg --config ui.strict=False an a
0: a
$ echo "[ui]" >> $HGRCPATH
$ echo "strict=True" >> $HGRCPATH
$ hg an a
hg: unknown command 'an'
(use 'hg help' for a list of commands)
[10]
$ hg annotate a
0: a
should succeed - up is an alias, not an abbreviation
$ hg up
0 files updated, 0 files merged, 0 files removed, 0 files unresolved