Revert "adapter: Create deterministic log index IDs (#30603)"

[ggevay]

This reverts commit 14cc787 to get around a release blocker issue: https://github.com/MaterializeInc/database-issues/issues/8799

Discussion here:
https://materializeinc.slack.com/archives/CTESPM7FU/p1732813333249199?thread_ts=1732808221.986649&cid=CTESPM7FU

Motivation

Tips for reviewer

Checklist

• This PR has adequate test coverage / QA involvement has been duly considered. (trigger-ci for additional test/nightly runs)
• This PR has an associated up-to-date design doc, is a design doc (template), or is sufficiently small to not require a design.
• If this PR evolves an existing $T ⇔ Proto$T mapping (possibly in a backwards-incompatible way), then it is tagged with a T-proto label.
• If this PR will require changes to cloud orchestration or tests, there is a companion cloud PR to account for those changes that is tagged with the release-blocker label (example).
• If this PR includes major user-facing behavior changes, I have pinged the relevant PM to schedule a changelog post.

[teskje]

I've added a second commit to add back the two removed proto fields. buf was complaining about them being removed and since we are planning to add these ID variants back, it seems easier to leave their proto fields and not use them than trying to convince buf to accept a breaking change.

[benesch]

On a hunch, I merged #30650 but I propose we hold off on merging this for a moment. I'm hopeful that the deterministic log ID migration will work in isolation, and then we can follow up with adding the LIR introspection sources in the next release.

[ggevay]

Ok, holding off on this one