Revert "tools build: Remove leftover libcap tests that prevents fast path feature detection from working"

Ian pointed out that the libcap feature test is also used by bpftool, so
we can't remove it just because perf stopped using it, revert the
removal of the feature test.

Since both perf and libcap uses the fast path feature detection
(tools/build/feature/test-all.c), probably the best thing is to keep
libcap-devel when building perf even it not being used there.

This reverts commit 47b3b643.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>