gendoc: do not strip 'hg ' from synopsis
This was an old left-over from when the synopsis line was used as a
header. We now have the command name by itself as the header and the
synopsis as a literal block immediately after..
Minimal hgk check
$ echo "[extensions]" >> $HGRCPATH
$ echo "hgk=" >> $HGRCPATH
$ hg init repo
$ cd repo
$ echo a > a
$ hg ci -Am adda
adding a
$ hg debug-cat-file commit 0
tree a0c8bcbbb45c
parent 000000000000
author test 0 0
committer test 0 0
revision 0
branch default
adda