Drop R2DBC BOM after 0.9 release

[mp911de]

Going forward, R2DBC 1.0 is expected to become the "done" version and a baseline for drivers for the foreseeable future. Having a bill of materials during the specification evolution helped to correlate driver versions to the specification version to ensure a consistent dependency arrangement.

With version 1.0 of the specification, we expect all available drivers to be based on that version which removes the need for version coordination. Additionally, BOM releases enforce a strong synchronization across participating drivers and BOM releases require constant release effort.

Therefore, I propose to stop releasing the BOM after the last 0.9 R2DBC release train, likely during the next year.

[mp911de]

We did not release a BOM, so we can close this ticket now.