encoder: h265: don't deprecate low-delay-b property
In !284 (merged), the low-delay-b property was deprecated. Some platforms can support both P-frames or low-delay-b, but the user has no way to enable low-delay-b on those platforms. It would be useful if the user can force low-delay-b to be used even when the platform supports P-frame. In many cases, low-delay-b can produce better quality.
Perhaps low-delay-b can be a tri-state property (auto, on, off), where auto is the default. On platforms that only support low-delay-b, then auto would turn it on. On platforms that support P-frames, auto would turn it off.
The other option is to keep it a true|false property where the default is true since all platforms should be able to support low-delay-b and generally produces better result.