Video recording unsupported on API<23

[aforcier]

I was looking at restoring the RECORD_AUDIO permission (#489, initially removed for API<23 in #488 to not prompt those users for a permission for an unreleased feature).

After restoring the permission however, I get this crash when recording video on API 21 or 22 devices:

com.automattic.loop E/AndroidRuntime: FATAL EXCEPTION: CameraX-video encoding thread
    Process: com.automattic.loop, PID: 8839
    java.lang.IllegalStateException
        at android.media.MediaCodec.native_dequeueOutputBuffer(Native Method)
        at android.media.MediaCodec.dequeueOutputBuffer(MediaCodec.java:1033)
        at androidx.camera.core.VideoCapture.videoEncode(VideoCapture.java:604)
        at androidx.camera.core.VideoCapture$2.run(VideoCapture.java:348)
        at android.os.Handler.handleCallback(Handler.java:739)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:135)
        at android.os.HandlerThread.run(HandlerThread.java:61)

Some research suggests that updating CameraX might help either resolve the issue or handle it better (I'm not sure which is the case).

We want to update CameraX when we can anyway (#197), though probably not in time for initial release.

For now (initial release) I suggest we do nothing. If we don't add the RECORD_AUDIO permission for API 21/22, attempting to record a video just fails silently. This is better than a crash or a rushed CameraX update that may cause bigger issues on all API levels.