select: remove unused MAX_SELECT_SECONDS

Remove the leftover from the commit 8ff3e8e8 ("select:
switch select() and poll() over to hrtimers").

Signed-off-by: Namhyung Kim <namhyung@gmail.com>
Acked-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>