staging: dgap: removes mgmt.h

This patch removes mgmt.h and the headers that include
it of files in dgap. This file isn't needed for the
driver to work with the kernel.

Signed-off-by: Lidza Louina <lidza.louina@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>