ion: remove ion_user_handle_t from ion_test.h

ion_test.h should not define ion_user_handle_t, and defining it
causes a warning:
In file included from drivers/staging/android/ion/ion_test.c:31:
drivers/staging/android/ion/../uapi/ion_test.h:23: error: redefinition of typedef 'ion_user_handle_t'
drivers/staging/android/ion/../uapi/ion.h:23: note: previous declaration of 'ion_user_handle_t' was here

Reported-by: Andrew Morton <akpm@linux-foundation.org>
Cc: John Stultz <john.stultz@linaro.org>
Signed-off-by: Colin Cross <ccross@android.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>