kvserver: remove TestReplicaRemovalClosesProposalQuota

[tbg]

As this test explained in its comment, the circumstances it was
seeking to test were very rarely met and even if the behavior
were missing, this wouldn't cause any problems.

The test has been skipped (accidentally) for a long time, was flaky even
then (leaking trace spans, see below), and it's not easy to
enact the situation the test wishes to construct in an idiomatic way.

It's pretty clear that the lines the test wants are present:

cockroach/pkg/kv/kvserver/replica_destroy.go

Lines 174 to 176 in 736a67e

	if pq := r.mu.proposalQuota; pq != nil {
	pq.Close("destroyed")
	}

It's better to remove the test at this point.

Closes #96932.

Also, fix a buglet that the test "accidentally" uncovered:

Previously, if evalAndPropose returned with an error while trying to
propose a pipelined write, it would leak the trace span.

Make sure this doesn't happen. The test that exercised this got deleted
in the previous commit, but this is still a bug that could cause a
larger leak if a condition were ever added to evalAndPropose which
could cause a large amount of errors (perhaps spread out over a longer
time period) in production clusters.

Unfortunately, writing a test for this is likely to be a net negative;
if the reviewer feels strongly I can add a testing knob to inject an
error in the right place in this method and exercise it that way.

Touches #96932.

Epic: none
Release note: None

[cockroach-teamcity]

This change is 

[tbg]

bors r=pavelkalinnikov

[craig]

Build succeeded:

• Bazel Essential CI (Cockroach)