alpha: remove the needless aliases osf_{readv,writev}

Commit 987f20a9 ("a.out: Remove the a.out implementation") removes
CONFIG_OSF4_COMPAT and its functionality. Hence, sys_osf_{readv,writev}
are now just aliases of sys_{readv,writev}.

Remove these needless aliases.

[ Identical patch also posted by Jason A. Donenfeld ]

Link: https://lore.kernel.org/lkml/CAHk-=wjwvBc3VQMNtUVUrMBVoMPSPu26OuatZ_+1gZ2m-PmmRA@mail.gmail.com/
Link: https://lore.kernel.org/all/20221004135301.1420873-1-Jason@zx2c4.com/


Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>