[3.0.x] UPnP: remove SAT>IP channel list fallback

When introducing SAT>IP support, we added a fallback mechanism on officially published channel lists in case the user neither specified a custom list nor the used set-top box provided one.

With the end of the SAT>IP Alliance that was dissolved 3 years ago, the fallback server is no longer available and there will be no replacement so this feature was removed.

Fixes #28684 (closed)

(cherry picked from commit 3df7b6e1, backport of !5681 (merged))