This reverts commit 421b592690.

The org.matrix.msc4143.rtc_foci property is indeed gone from MSC4143 and
Element Call v0.24.0 no longer reads it, but Element Web does not ship that
version of Element Call yet. v1.12.26 embeds Element Call v0.22.0, which
discovers transports through the well-known property.

That embedded copy cannot consult the homeserver's RTC transports API
instead: it runs as a widget, a widget holds no access token and the API
requires authentication, so its own discovery code skips the API branch
outright. Newer Element Call versions ask their host client over the widget
API (MSC4515) and Element Web already implements that side of it, but the
widget has to speak it too.

Dropping the property therefore left Element Web and Element Desktop users
with MISSING_MATRIX_RTC_TRANSPORT when starting a call.

The restored variables carry a comment about why the property stays, and the
changelog entry is rewritten to announce the revert.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>