arch,sim: Drop the syscall number from the syscall func signature.

arch,sim: Drop the syscall number from the syscall func signature.

This value is almost never used, and is now part of the SyscallDesc.

Change-Id: Ia4ffc19774bb2eac8f29134e3765c06a264407b6
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/24118
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>