perf debug: Remove needless include directives from debug.h

All we need there is a forward declaration for 'union perf_event', so
remove it from there and add missing header directives in places using
things from this indirect include.

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-7ftk0ztstqub1tirjj8o8xbl@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-ftrace.c

@@ -13,8 +13,10 @@
 #include <fcntl.h>
 #include <poll.h>
 #include <linux/capability.h>
+#include <linux/string.h>
 
 #include "debug.h"
+#include <subcmd/pager.h>
 #include <subcmd/parse-options.h>
 #include <api/fs/tracing_path.h>
 #include "evlist.h"
@@ -24,7 +26,6 @@
 #include "util/cap.h"
 #include "util/config.h"
 
-
 #define DEFAULT_TRACER  "function_graph"
 
 struct perf_ftrace {