ipc/shm: uapi: remove dependency on libc

ipc/shm: uapi: remove dependency on libc

Using libc types and headers from the UAPI headers is problematic as it
introduces a dependency on a full C toolchain.  shm.h does not even use
any symbols from the libc header as the usage of getpagesize() was removed
a decade ago in commit 060028bac94b ("ipc/shm.c: increase the defaults for
SHMALL, SHMMAX")

Drop the unnecessary inclusion.

Link: https://lkml.kernel.org/r/20251222-uapi-shm-v1-1-270bb7f75d97@linutronix.de
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>