From: Arnd Bergmann <arnd@arndb.de>

Dave Jones already removed some of the useless __KERNEL_SYSCALLS__ defines
in various files, this gets rid of almost all the others.  Replacing
execve() is nontrivial, so I left those in for now.

For all the other system calls that are currently used from inside the
kernel, calling the sys_* function directly should always have an identical
effect.