perf tools: Remove distclean from Makefile help output

distclean as an alias for clean was removed from the perf Makefile by
commit a3d1ee10

However, that commit neglected to remove it from the help output of
the perf Makefile, which could result in a user trying the following.

$ cd tools/perf/
$ make help | grep distclean
  distclean		- alias to clean
$ make distclean
make: *** No rule to make target `distclean'.  Stop.

This patch removes it from the Makefile help output.

Link: http://lkml.kernel.org/r/1328134591-19851-1-git-send-email-jkacur@redhat.com


Signed-off-by: John Kacur <jkacur@redhat.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>