Advanced Search on relay search has selected the obfs4 transport as default

After the fixes for #40093 (closed) landed our Advanced Search regressed as the obfs4 transport is selected by default. In fact, there is no option to not include any transport at all. If I want to just see all relays that joined during the last 7 days I am not executing something like https://metrics.torproject.org/rs.html#search/type:relay%20first_seen_days:0-7%20transport:obfs4?fields=transports, which, somewhat surprisingly, gives 0 results.

We should have by default something like Any for the transports, I guess.