perf_event: Eliminate raw->size

raw->size is not used, this patch just cleans it up.

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Li Zefan <lizf@cn.fujitsu.com>
LKML-Reference: <4B1C8CC4.4050007@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>