Revert "VLCSampleBufferDisplay: remove empty Display callback"
This reverts commit 5c06e543.
The core is sending pictures too fast in this mode.
Even the Android display mode which can use the display date has a display callback forcing the core to wait between pictures.
Ultimately we should try to make this work, assuming the date handling in the Prepare is more accurate (for example on Windows which has a few milliseconds of precision).