Remove drmmode_crtc_private_rec::present_vblank_* related code

Not needed anymore with the more robust mechanisms for preventing nested
drmHandleEvent calls introduced in the previous changes.

(Ported from amdgpu commit 85cd8eef0cbed7b409b07f58d76dacd34aa3ddea)
Acked-by: Alex Deucher <alexander.deucher@amd.com>