Remove the Android 2.x/3.x support code.

The Android 4.x+ code has changed a lot since the initial import
of the eyes-free codebase. A lot of bug fixes and improvements
have been made to it.

The eyes-free codebase had two different code paths:
  *  one for ICS (4.0) or later, using the Java-based TTS APIs
     provided by the Android platform;
  *  one for pre-ICS using an internal C++-based TTS API.

Thus, any bug fixes or improvements would have to be done to both
code bases if Android 2.x/3.x support is required. This is not
maintainable.

If pre-ICS support is to be re-added in the future, the plan will
be to:
  *  forward the C++-based APIs to the Java-based APIs via a
     compatibility layer;
  *  use a compatibility layer (Android Support Library?) for using
     the ICS settings API on pre-ICS.