recorder: use video input as source

MediaRecorder no longer uses VideoSender (encoder) as a source for its
local video and will directly use VideoInput (decoder), as it is earlier
in the pipeline.

This is the first step to support switching inputs while recording.

Change-Id: Ia163efa3b20a349a93fc7b05213ec5e00de1704e
Reviewed-by: Sebastien Blin <sebastien.blin@savoirfairelinux.com>