This reverts commit 27925032.
Conflicts:
	g

According to vmiklos, that commit was meant to help with the following scenario:
Assume a dev uses submodules and uses plain `git pull && git submodule update`
instead of ./g.  When they forget the "&& git submodule update" part and do
`git commit -a`, changes to the submodules were excluded from the commit.

However, when they do `git add -u && git commit` instead of `git commit -a`,
changes to the submodules /are/ included in the commit, despite `git status` or
`git diff` (both prior to `git add -u`) or `git diff --cached` (after `git add
-u`) not indicating that there are any changes to the submodules.  I consider
that problem more confusing and severe than the problem that the commit solved.

Change-Id: I595eed3c1c04efd108be1ccd792d8d7bce72a345
Reviewed-on: https://gerrit.libreoffice.org/51155Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>