perf build: Remove Makefile.syscalls

Now a single beauty file is generated and used by all architectures,
remove the per-architecture Makefiles, Kbuild files and previous
generator script.

Note: there was conversation with Charlie Jenkins
<charlie@rivosinc.com> and they'd written an alternate approach to
support multiple architectures:
https://lore.kernel.org/all/20250114-perf_syscall_arch_runtime-v1-1-5b304e408e11@rivosinc.com/
It would have been better to have helped Charlie fix their series (my
apologies) but they agreed that the approach taken here was likely
best for longer term maintainability:
https://lore.kernel.org/lkml/Z6Jk_UN9i69QGqUj@ghost/



Signed-off-by: Ian Rogers <irogers@google.com>
Reviewed-by: Howard Chu <howardchu95@gmail.com>
Reviewed-by: Charlie Jenkins <charlie@rivosinc.com>
Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Arnaldo Carvalho de Melo <acme@kernel.org>
Link: https://lore.kernel.org/r/20250319050741.269828-11-irogers@google.com


Signed-off-by: Namhyung Kim <namhyung@kernel.org>