perf: Remove duplicated workqueue.h include from perf_event.h

It is already included a little bit higher up in that file.
Signed-off-by: NYueHaibing <yuehaibing@huawei.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20190117072504.14428-1-yuehaibing@huawei.comSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>

include/linux/perf_event.h

@@ -53,7 +53,6 @@ struct perf_guest_info_callbacks {
 #include <linux/atomic.h>
 #include <linux/sysfs.h>
 #include <linux/perf_regs.h>
-#include <linux/workqueue.h>
 #include <linux/cgroup.h>
 #include <asm/local.h>