Editor (flex branch) attempts to fetch flex-only tables for non-flex feeds

[binh-dam-ibigroup]

Observed behavior

This error message is shown when opening an editor initialized by a non-flex branch using the editor from the flex branch,
and editing features are greyed out (disabled).

Error fetching GTFS entities via GraphQL

- Exception while fetching data (/feed/booking_rules) : org.postgresql.util.PSQLException: ERROR: relation "dbxp_rktgmydoiwrwvebtjtbprv.booking_rules" does not exist
  Position: 15 ({"line":18,"column":11})
- Exception while fetching data (/feed/locations) : org.postgresql.util.PSQLException: ERROR: relation "dbxp_rktgmydoiwrwvebtjtbprv.locations" does not exist
  Position: 15 ({"line":52,"column":11})

Expected behavior

No error message should be shown, and editing features should be enabled.

Steps to reproduce the problem (locally)

1. Checkout a non-flex branch and start datatools
2. Create a non-flex feed, and import a non-flex feed
3. Start editing the imported feed.
4. Stop datatools. Checkout a flex branch and start datatools again.
5. Start editing the feed above.
6. Observe the error message shown above.

Any special notes on configuration used

NA

Version of datatools-server and datatools-ui if applicable (exact commit hash or branch name)

Datatools server dev vs. branch with #439.