alpha/osf_sys: remove unused MAX_SELECT_SECONDS

Remove the leftover from the commit 14e2acd8 ("select:
fix alpha OSF wrapper").

Signed-off-by: Namhyung Kim <namhyung@gmail.com>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Matt Turner <mattst88@gmail.com>