Remove check for useSIGIO option

Commit 6a5a4e60 removed the option to
configure useSIGIO option. Indeed, the xfree86 SIGIO support was
reworked to use internal versions of OsBlockSIGIO and OsReleaseSIGIO.

As a result, useSIGIO is no longer needed and can dropped

Fixes: 6a5a4e60 - Remove SIGIO support for input [v5]
Closes: xorg/xserver#1107
Reviewed-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Prabhu Sundararaj <prabhu.sundararaj@nxp.com>
Signed-off-by: Mylène Josserand <mylene.josserand@free-electrons.com>
Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
4 jobs for fix-sigio in 4 minutes and 32 seconds (queued for 1 second)