gitcli: drop mention of “non-dashed form”

gitcli: drop mention of “non-dashed form”

Git builtins used to be called like e.g. `git-commit`, not `git
commit` (*dashed form* and *non-dashed form*, respectively). The dashed
form was deprecated in version 1.5.4 (2006). Now only a few commands
have an alternative dashed form when `SKIP_DASHED_BUILT_INS` is
active.[1]

The mention here is from 2f7ee089dff (parse-options: Add a gitcli(5) man
page., 2007-12-13), back when the deprecation was relatively
recent. These days though it seems like an irrelevant point to make to
budding CLI scripters—you don’t have to warn against a style that
probably doesn’t even work on their git(1) installation.

† 1: 179227d6e21 (Optionally skip linking/copying the built-ins,
    2020-09-21)

Signed-off-by: Kristoffer Haugsbakk <code@khaugsbakk.name>
Signed-off-by: Junio C Hamano <gitster@pobox.com>