sh: kprobes: Merge arch_copy_kprobe() into arch_prepare_kprobe()

sh: kprobes: Merge arch_copy_kprobe() into arch_prepare_kprobe()

arch/sh/kernel/kprobes.c:52:16: warning: no previous prototype for 'arch_copy_kprobe' [-Wmissing-prototypes]

Although SH kprobes support was only merged in v2.6.28, it missed the
earlier removal of the arch_copy_kprobe() callback in v2.6.15.

Based on the powerpc part of commit 49a2a1b83ba6fa40 ("[PATCH] kprobes:
changed from using spinlock to mutex").

Fixes: d39f5450146ff39f ("sh: Add kprobes support.")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Link: https://lore.kernel.org/r/717d47a19689cc944fae6e981a1ad7cae1642c89.1709326528.git.geert+renesas@glider.be
Signed-off-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>