sql: deflake TestTrace

This has been seen to flake in CI:

```
=== RUN   TestTrace/ShowTraceForVectorized/TracingOff/node-1
    trace_test.go:386: expected span: "session recording", got: "pendingLeaseRequest: requesting lease"
    trace_test.go:397: remaining span: "session recording"
    trace_test.go:397: remaining span: "sql query"
    trace_test.go:397: remaining span: "sql txn"
    trace_test.go:397: remaining span: "txn coordinator send"
            --- FAIL: TestTrace/ShowTraceForVectorized/TracingOff/node-1 (0.02s)
```

There was already an exception for this span, but with a `storage.`
prefix. This patch removes the prefix.

This flake has possibly been made worse with the introduction of a
metamorphic setting to only use expiration-based leases in ecc931b.

Epic: none
Release note: None

pkg/sql/trace_test.go

@@ -45,7 +45,7 @@ func TestTrace(t *testing.T) {
 	// These are always appended, even without the test specifying it.
 	alwaysOptionalSpans := []string{
 		"drain",
-		"storage.pendingLeaseRequest: requesting lease",
+		"pendingLeaseRequest: requesting lease",
 		"storage.Store: gossip on capacity change",
 		"outbox",
 		"request range lease",