staging: lustre: llite: rw26: Remove unused function definition

The patch removes unused function definition ll_get_user_pages().
The use of ll_get_user_pages() was replaced with iov_iter_get_pages_alloc()
in commit 91f79c43.

Signed-off-by: sayli karnik <karniksayli1995@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>