perf tools: Remove annoying extra message from the features build

This message:

  Makefile:153: The path 'python-config' is not executable.

Appears on every perf build that does not have a sufficient python
environment installed. It's really just an internal detail of python
configuration pass and users should not see it - and it's pretty
meaningless to them in any case because the message is not very helpful.
(So it's not executable. Why does that matter? What can the user do
about it?)

Remove the warning, the missing python feature warning is sufficient:

  config/Makefile:566: No python-config tool was found
  config/Makefile:566: Python support will not be built

although even that one isn't very helpful to users: so no Python support
will be built, what can the user do to fix that? Most other such
warnings give package install suggestions.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: David Ahern <david.ahern@oracle.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/20150228081750.GA31887@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>