Avoid reusing released decoders after SetDecoders()

SetDecoders() only deregistered decoders that were removed or changed,
but it also reset the decoder database's active payload type. The next
frame then released the active decoder and configured the same instance
again. Not all decoders support that: Chromium's hardware decoders fail
Configure() after Release() and permanently fall back to software
decoding. This happens e.g. when the receiving side creates a new offer,
since that typically changes the set of receive codecs.

Deregister all of the previous decoders instead, so that the factory
creates new instances on demand. This matches how decoders were handled
before the receive stream stopped being recreated on decoder changes
(https://webrtc-review.googlesource.com/c/src/+/494540).

Bug: chromium:572220780
Change-Id: Ibe646151c9803aab1e01665b8a70352f09e5c101
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/508961
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#48904}