concurrency: remove the concept of distinguished waiters

[arulajmani]

Now that https://github.com/cockroachdb/cockroach/pull/119581 has landed, we no longer distinguish (no pun intended) between liveness pushes and deadlock detection pushes. This obviates the need for the concept of distinguished waiters. Removing them also serves as a nice cleanup, and gets us a step closer to things like generalized lock promotion.

Informs https://github.com/cockroachdb/cockroach/issues/110435

Release note: None

[blathers-crl[bot]]

Your pull request contains more than 1000 changes. It is strongly encouraged to split big PRs into smaller chunks.

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[cockroach-teamcity]

This change is 

[craig[bot]]

Build failed:

• Bazel Essential CI (Cockroach)

[arulajmani]

Data-driven tests skewed post rebase. I'll try again.

bors r=nvanbenschoten

[craig[bot]]

Build succeeded:

• Bazel Essential CI (Cockroach)