m68k: Remove ptrace_signal_deliver

This fixes debugger syscall restart interactions.  A debugger that
modifies the tracee's program counter is expected to set the orig_d0
pseudo register to -1, to disable a possible syscall restart.

This removes the last user of the ptrace_signal_deliver hook in the ptrace
signal handling, so remove that as well.

Signed-off-by: Andreas Schwab <schwab@linux-m68k.org>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>