Revert "Handle SDL grabs failing (Mark McLoughlin)"

This reverts commit 6bb816031f8bc0aafc3476e6dfa4293ee3a5f106.

SDL_WM_GrabInput does not reliably bail out if grabbing is impossible.
So if we get here, we already lost and will block. But this can no
longer happen due to the check in sdl_grab_start. So this patch became
obsolete.

Conflicts:

	sdl.c

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
