Exception when performing the global gestrue to enable accessibility.

1. If there is a non-speaking accessibility service installed and the
   global gesture is performed an exception is thrown since an attempt
   is made to modify the list with services returned by the accessibility
   manager (to remove the non-speaking ones) but this list is immutable.
   Now the returned services are put into a mutable list before removing
   the non-speaking ones.

bug:7280996

Change-Id: I2852a3e169c1d34d942b50fb439e0961394c92bc