perf tools: Drop prefetch.h

This was needed at the time before e66eed651fd1 ("list: remove
prefetching from regular list iterators") where the list iterators did
prefetch elements. This turned out to be counter-productive and hurt
performance and they were removed. Which makes the prefetch.h header
unused so drop it.

Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: David Ahern <dsahern@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Robert Richter <rric@kernel.org>
Link: http://lkml.kernel.org/r/1391611914-26054-4-git-send-email-bp@alien8.de
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>