This was never gone and the feature is not finished yet (bug 1629788 comment 27). Some other patches still await review.
VAAPI was just temporarily disabled: bug 1645706 disabled the dmabuf-video-textures pref that VAAPI now depends upon. You had to enable two prefs for VAAPI. bug 1646051 changed it to let the VAAPI pref also enable dmabuf-video-textures. You see this bug again because you are using VAAPI again.
This was never gone and the feature is not finished yet (bug 1629788 comment 27). Some other patches still await review. video-textures pref that VAAPI now depends upon. You had to enable two prefs for VAAPI. bug 1646051 changed it to let the VAAPI pref also enable dmabuf- video-textures. You see this bug again because you are using VAAPI again.
VAAPI was just temporarily disabled: bug 1645706 disabled the dmabuf-