Documentation/git-reset: don't mention --mixed for selected-paths reset

The option is accepted, but that is the only form selected-paths
variant of the reset command takes, so there is no point mentioning it.
And while we're at it, use the dashless git call.
Signed-off-by: NPieter de Bie <pdebie@ai.rug.nl>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/git-reset.txt

@@ -8,8 +8,8 @@ git-reset - Reset current HEAD to the specified state
 SYNOPSIS
 --------
 [verse]
-'git-reset' [--mixed | --soft | --hard] [-q] [<commit>]
-'git-reset' [--mixed] [-q] [<commit>] [--] <paths>...
+'git reset' [--mixed | --soft | --hard] [-q] [<commit>]
+'git reset' [-q] [<commit>] [--] <paths>...
 
 DESCRIPTION
 -----------