perf tools: Move event synthesizing routines to separate header

Those are the only routines using the perf_event__handler_t typedef and
are all related, so move to a separate header to reduce the header
dependency tree, lots of places were getting event.h and even stdio.h,
limits.h indirectly, so fix those as well.

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-yvx9u1mf7baq6cu1abfhbqgs@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/session.h

@@ -138,9 +138,4 @@ int perf_session__deliver_synth_event(struct perf_session *session,
 int perf_event__process_id_index(struct perf_session *session,
 				 union perf_event *event);
 
-int perf_event__synthesize_id_index(struct perf_tool *tool,
-				    perf_event__handler_t process,
-				    struct evlist *evlist,
-				    struct machine *machine);
-
 #endif /* __PERF_SESSION_H */