perf event: Drop perf_regs.h include, not needed anymore

Since commit c8978997 ("perf tools: Prevent out-of-bounds access
to registers") the util/event.h header doesn't use anything from
util/perf_regs.h, so drop it to untangle the header dependency tree a
bit, speeding up compilation.
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/event.h

@@ -12,8 +12,6 @@
 #include <perf/event.h>
 #include <linux/types.h>
 
-#include "perf_regs.h"
-
 struct dso;
 struct machine;
 struct perf_event_attr;