avformat/riffenc: don't force WAVEFORMATEXTENSIBLE for flt/dbl LPCM
2c2a167ca7 forced WAVEFORMATEXTENSIBLE for all LPCM streams with greater
than 16 bits per sample. However, WAVEFORMATEX allows IEEE Float samples
or any depth where raw depth == coded depth, see Remarks section at
https://learn.microsoft.com/en-us/windows/win32/api/mmreg/ns-mmreg-waveformatex
and samples M1F1-float32-AFsp, M1F1-float64-AFsp at
https://www.mmsp.ece.mcgill.ca/Documents/AudioFormats/WAVE/Samples.html
There are hardware devices and likely software players requiring float samples
that fail to qualify files with WAVEFORMATEXTENSIBLE headers.
