libtraceevent: Remove hard coded include to /usr/local/include in Makefile

having /usr/local/include hardcoded into the makefile is not necessary
as this is automatically included by GCC. It also infects cross-compile
builds with the host systems includes.

Signed-off-by: Jack Mitchell <jack.mitchell@dbbroadcast.co.uk>
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/1362741712-21308-1-git-send-email-ml@communistcode.co.uk
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>