staging: dgap: Remove some dead code

This patch removes more dead code and code associated
with that dead code. The from_user variable in the
dgap_tty_write function was never true. The code under
its test was never being executed. So variables and
functions supporting only that code are also dead.

Signed-off-by: Mark Hounschell <markh@compro.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>