Revert recent changes to the caught-up checks

[teskje]

This reverts two recent changes made to the caught-up checks. Because subsources don't emit status updates when no data flows through them, these changes could cause 0dt deployments to get stuck in the face of low-traffic sources.

Reverted changes:

• storage,0dt: include source exports (aka. subsources) in hydration checks #33589
• adapter: filter out non-active storage collections in caught_up checks #33672

Motivation

• This PR fixes a recognized bug.

Fixes https://github.com/MaterializeInc/database-issues/issues/9721

Tips for reviewer

See Slack thread.

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.