flex: remove obsolete disable-tests.patch

flex: remove obsolete disable-tests.patch

We added this because automake was causing things to be built, but now
this doesn't seem to be the case:

  all: all-am

  all-am: Makefile $(SCRIPTS)

  SCRIPTS = $(dist_noinst_SCRIPTS)

  dist_noinst_SCRIPTS = tableopts.sh

tableopts.sh is a source file that is both in the tarballs and git.

Thus, remove the patch.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>