perf tools: Remove unneeded include

There is no point in sort.h including itself.

The include was added when the file was created, in commit "perf tools:
Create util/sort.and use it" (dd68ada2

) and added a include to "sort.h"
in lot of files (all the files that started using the file). It was
probably added by mistake on sort.h too.

Signed-off-by: Rodrigo Campos <rodrigo@sdfg.com.ar>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1383776454-10595-1-git-send-email-rodrigo@sdfg.com.ar
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>