Recorder: set minSdk to api 29 and cleanup

We are using MediaProvider now, which is unavailable
on api level < 29.
Moreover the aosp build env already sets the minSdk to
the current api level if unspecified.

Let's drop compatibility code and cleanup

Signed-off-by: Joey <joey@lineageos.org>
Change-Id: I13570f47d733a3f5be8c1d0c42ef60892f4971c9