bpftool: Remove useless #include to <perf-sys.h> from map_perf_ring.c

bpftool: Remove useless #include to <perf-sys.h> from map_perf_ring.c

The header is no longer needed since the event_pipe implementation
was updated to rely on libbpf's perf_buffer. This makes bpftool free of
dependencies to perf files, and we can update the Makefile accordingly.

Fixes: 3d5ce88be95a ("tools/bpftool: switch map event_pipe to libbpf's perf_buffer")
Signed-off-by: Quentin Monnet <quentin@isovalent.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20211020094826.16046-1-quentin@isovalent.com