Do the lazy loading check in the batch of things we do before
starting a sync rather than at client start time, so we don't fail
to start the client if we can't hit the HS to determine LL support.
Fixes https://github.com/vector-im/riot-web/issues/7455
the sync data needs to be cleared toggling in both directions:
not LL -> LL: you want to get rid of all the excess state in the
sync data to get the RAM benefits
LL -> not LL: you want to fill the sync data state again
because getOutOfBandMembers won't be called