Remove the redundant QTEST_ACCESSIBILITY define.

Remove the redundant QTEST_ACCESSIBILITY define.

QTEST_ACCESSIBILITY was always defined and only used in one autotest.
Code that uses accessibility features should be excluded if Qt was built
without accessibility rather than based on a define in the test
framework.

Change-Id: I3a517a579a51f536a0983b43bd99e86292026552
Reviewed-by: pending
Reviewed-on: http://codereview.qt.nokia.com/129
Reviewed-by: Morten Johan Sørvig <morten.sorvig@nokia.com>
Reviewed-by: Rohan McGovern <rohan.mcgovern@nokia.com>