[Closed by !3137; Version-unspecific] Deprecate QueryObservedTx BlockHeight and FinaliseHeight

[Version-unspecific]

[2023-05-03 update: Issue #1522 (closed) submitted for this.]

!2748 (merged)/!2681 (merged) 'QueryObservedTx and QueryTxSigners' was implemented in network version 1.106.0,
and renamed the block_height and finalise_height fields additively by keeping them and adding differently-named duplicate fields,
respectively external_observed_height and external_confirmation_delay_height.

From the discussion of when the previous fields would be deprecated ( @ursa9r ):

[...]deprecated 2 versions later (v1.105 if this is tagged for v1.103)? Then once this is live we can send an alert to interfaces to update so this can roll out seamlessly while also avoiding the extra hassles of versioned endpoints.

Assuming this deprecation MR is included in network version 1.110.0 at the earliest,
that would be 4 versions between duplication and deprecation.
(I am thus particularly glad that a specific version for deprecation was not included in the openapi.yaml descriptions.)

When version 1.106.0 was released, was there an alert sent to interfaces as planned?
If not, perhaps such an alert could be sent now and this merge request milestoned for 1.112.0 so that it isn't forgotten.