Documentation: spell 'git cmd' without dash throughout

The documentation was quite inconsistent when spelling 'git cmd' if it
only refers to the program, not to some specific invocation syntax:
both 'git-cmd' and 'git cmd' spellings exist.

The current trend goes towards dashless forms, and there is precedent
in 647ac70 (git-svn.txt: stop using dash-form of commands.,
2009-07-07) to actively eliminate the dashed variants.

Replace 'git-cmd' with 'git cmd' throughout, except where git-shell,
git-cvsserver, git-upload-pack, git-receive-pack, and
git-upload-archive are concerned, because those really live in the
$PATH.

Documentation/git-submodule.txt

@@ -99,11 +99,11 @@ locate the submodule using the relative URL in .gitmodules.
 status::
 	Show the status of the submodules. This will print the SHA-1 of the
 	currently checked out commit for each submodule, along with the
-	submodule path and the output of 'git-describe' for the
+	submodule path and the output of 'git describe' for the
 	SHA-1. Each SHA-1 will be prefixed with `-` if the submodule is not
 	initialized and `+` if the currently checked out submodule commit
 	does not match the SHA-1 found in the index of the containing
-	repository. This command is the default command for 'git-submodule'.
+	repository. This command is the default command for 'git submodule'.
 +
 If '--recursive' is specified, this command will recurse into nested
 submodules, and show their status as well.