bison deprecated the "%pure-parser" directive in favor of "%define
api.pure full".

The api.pure got introduced in bison 2.3 (Oct 2007), so it seems safe to
use it without any version check.
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lore.kernel.org/lkml/20200112192259.GA35080@kravaSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>