arm64: Remove unimplemented syscall log message

arm64: Remove unimplemented syscall log message

Stop printing a (ratelimited) kernel message for each instance of an
unimplemented syscall being called. Userland making an unimplemented
syscall is not necessarily misbehaviour and to be expected with a
current userland running on an older kernel. Also, the current message
looks scary to users but does not actually indicate a real problem nor
help them narrow down the cause. Just rely on sys_ni_syscall() to return
-ENOSYS.

Cc: <[email protected]>
Acked-by: Will Deacon <[email protected]>
Signed-off-by: Michael Weiser <[email protected]>
Signed-off-by: Will Deacon <[email protected]>