Contrary to the initial intention (in rB9916e0193c36), `TREDRAW_SOFT`
flag, when isolated, is not cleared in `transformApply` and therefore is
used in the `drawTransformApply` callback which basically recalculates
the `transformation` which finally clears the flag.
So remove the `drawTransformApply` callback so `transformApply` is not
called when unnecessary.
Differential Revision: https://developer.blender.org/D14430