zsh_completion: rename _hg_style_opts to _hg_template_opts
--style is a deprecated alias for --template, and doesn't show up in help
without --verbose, so completing it doesn't make much sense.
Let's s/style/template/ this variable to be more consistent with cmdutil.py,
which is helpful to look at in parallel next time someone wants to update the
completion rules.
Differential Revision: https://phab.mercurial-scm.org/D4261
Set up
$ hg init repo
$ cd repo
Try to import an empty patch
$ hg import --no-commit - <<EOF
> EOF
applying patch from stdin
abort: stdin: no diffs found
[255]
No dirstate backups are left behind
$ ls .hg/dirstate* | sort
.hg/dirstate