Repair transactionality of `st_client` removals after disconnect

[Centril]

Description of Changes

Fixes https://github.com/clockworklabs/SpacetimeDB/issues/2390.

API and ABI breaking changes

None

Expected complexity level and risk

2

Testing

Not tested as of yet. To my knowledge, we don't really have the test infra to force the disconnect and then check the TxData.