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 2f7ee08 (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: 179227d (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>

Author: LemmingAvalanche

Documentation/gitcli.txt

@@ -81,9 +81,6 @@ you will.
 Here are the rules regarding the "flags" that you should follow when you are
 scripting Git:
 
- * It's preferred to use the non-dashed form of Git commands, which means that
-   you should prefer `git foo` to `git-foo`.
-
  * Splitting short options to separate words (prefer `git foo -a -b`
    to `git foo -ab`, the latter may not even work).