Remove compatible sigset structure: as it has the same size for both
32-bit and 64-bit, I didn't use it across the code, only for a size check.
The check is removed as we use now only k_rtsigset_t.
Wordsize for sigset is changed to 64-bit - as it's written in comment
for possible 32-bit native building.

If we ever going to support compat mode for other archs, we will
need to re-introduce compat_sigset_t type if it has for those archs
different sizes for compat/native builds.
But for a while, let's simplify this.

travis-ci: success for Compel/compat cleanups
Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Acked-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>