powerpc: remove unused *_syscall_64.o variables in Makefile

powerpc: remove unused *_syscall_64.o variables in Makefile

Commit ab1a517d55b0 ("powerpc/syscall: Rename syscall_64.c into
interrupt.c") missed to update these three lines:

  GCOV_PROFILE_syscall_64.o := n
  KCOV_INSTRUMENT_syscall_64.o := n
  UBSAN_SANITIZE_syscall_64.o := n

To restore the original behavior, we could replace them with:

  GCOV_PROFILE_interrupt.o := n
  KCOV_INSTRUMENT_interrupt.o := n
  UBSAN_SANITIZE_interrupt.o := n

However, nobody has noticed the functional change in the past three
years, so they were unneeded.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240216135517.2002749-1-masahiroy@kernel.org