Remove custom sort implementation in QTriangulator in favour of std::sort.

Remove custom sort implementation in QTriangulator in favour of std::sort.

qSort has terrible performance, especially on mostly-sorted input, which is
presumably why a custom implementation was created. However, std::sort has much
better performance than qSort in many cases.

Benchmarking shows that std::sort beats out the custom sort by a very narrow
margin (21-22ms for qSort, 14-15ms for sort, 14ms for std::sort) in a simple
benchmark of sorting.

Change-Id: If7e57fdfaf98e741d1621969461537c82f9169fe
Reviewed-by: Kim M. Kalland <kim.kalland@nokia.com>
Reviewed-by: Gunnar Sletta <gunnar.sletta@nokia.com>