perf header: Properly warn/print when libtraceevent/libbpf support is missing

perf header: Properly warn/print when libtraceevent/libbpf support is missing

By removing the features from feat_ops with ifdefs the previous logic
would print "# (null)" when perf processed a feature that lacked
builtin support. Remove the ifdefs from feat_ops and in the relevant
functions print errors/messages about the lack of support.

Signed-off-by: Ian Rogers <irogers@google.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>