OPUS codec does not support sample rate of 44100

[PatrykMis]

44100 sample rate should be removed from constants and at least set by if statement which checks for chosen encoder/format.

Current implementation, if set to OPUS, saves recording in 48000 causing playback to be 4% faster than it should be. It is very audible and also noticeable in recording length.

The solution is to set recording sample rate strictly to 48000 if user choose OPUS, or to provide resampling (https://developer.android.com/ndk/guides/audio/sampling-audio).

I will check if I will be able to do first solution myself and create pull request for it.