perf pmu: Remove needless evsel.h include, only needs one fwd decl

To reduce the header dependency tree.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-rc389o1z0htwukqv6ni1viun@git.kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>