Revert "Fix compilation for Android ARMv5"

This reverts commit 9fa1bdeeb2bca6f9ba370fce594a47a066a7e81a which
is no longer needed because the Android NDK now contains a
toolchain without the bug for which it was a work-around.

Task-number: QTBUG-31051
Change-Id: I601ba2fccb927ee7e818644de4474700e2eec8f1
Reviewed-by: BogDan Vatra <bogdan@kde.org>
Use custom class for storing distance fields instead of QImage.

Distance fields are stored using a one-byte alpha component per pixel, a
format that QImage doesn't currently support. The Indexed8 format was used
instead, limiting what could be done with the QImage.
This patch introduces a new private class, QDistanceField, with a similar
API to QImage and using the Alpha8 pixel format. Unlike QImage which
aligns scanlines on a 4-byte boundary, QDistanceField tightly packs
scanlines together.

Task-number: QTBUG-30908
Task-number: QTBUG-32861
Change-Id: Ic273259ea07dfbd2b81a6358c0ca11a2330eb749
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>