docs: do not document the `git remote-testgit` command

Since 7ded055401 (build: do not install git-remote-testgit, 2013-06-07),
we do not install it. Therefore it makes no sense to document it,
either.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-remote-testgit.txt

@@ -1,30 +0,0 @@
-git-remote-testgit(1)
-=====================
-
-NAME
-----
-git-remote-testgit - Example remote-helper
-
-
-SYNOPSIS
---------
-[verse]
-git clone testgit::<source-repo> [<destination>]
-
-DESCRIPTION
------------
-
-This command is a simple remote-helper, that is used both as a
-testcase for the remote-helper functionality, and as an example to
-show remote-helper authors one possible implementation.
-
-The best way to learn more is to read the comments and source code in
-'git-remote-testgit'.
-
-SEE ALSO
---------
-linkgit:gitremote-helpers[7]
-
-GIT
----
-Part of the linkgit:git[1] suite

Documentation/gitremote-helpers.txt

@@ -513,8 +513,6 @@ linkgit:git-remote-ext[1]
 
 linkgit:git-remote-fd[1]
 
-linkgit:git-remote-testgit[1]
-
 linkgit:git-fast-import[1]
 
 GIT