*: evaluate uses of `skip.Stress()`

[rickystewart]

With the RBE-based CI and nightlies, this variable will not be set in CI, which means that skip.Stress() will always return false. The following uses of it should be evaluated and maybe replaced with alternatives.

cockroach$ rg skip.Stress
pkg/sql/plan_opt_test.go
118:		if !skip.Stress() {

pkg/sql/mvcc_statistics_update_job_test.go
211:		if skip.Stress() {

pkg/ccl/streamingccl/replicationtestutils/testutils.go
494:	if skip.Stress() || util.RaceEnabled {

pkg/ccl/kvccl/kvtenantccl/upgradeinterlockccl/local_test_util_test.go
113:		if skip.Stress() {

See also: #123907 #123908

Jira issue: CRDB-38598

[rickystewart]

For now I'm keeping this in T-dev-inf so the thing doesn't get lost.