Remove unused Qt 6 sensors gesture code

The commit https://codereview.qt-project.org/c/qt/qtsensors/+/363735
disabled the gesture code in Qt 6.

This task is about removing them on the dev branch to avoid distraction when keeping the codebase up-to-date.

If, and in whichever shape or form the gestures may make a comeback, the code can be found in earlier branches and git history for reference.