mot-encoder: fix transmission of DLS when slides are enabled
Revert "Write DSE at start of AU"

This reverts commit 05e6de86461b4ab0c55880db0c83d7a7bd6c5bc1 which
broke audio decoding for PURE One Elite receivers, but fixed
slideshow and DLS decoding on PURE Sensia receivers.

Slides and DLS are now not working on PURE Sensia, but at least
audio is working again.