fix clippy --release failure introduced in #4030

PR  `build: run clippy for powerset of features (#4077)`
brought us a `clippy --release` pass.

It was merged after #4030, which fails under `clippy --release` with

```
error: static `TENANT_ID_EXTRACTOR` is never used
    --> pageserver/src/tenant/timeline.rs:4270:16
     |
4270 |     pub static TENANT_ID_EXTRACTOR: once_cell::sync::Lazy<
     |                ^^^^^^^^^^^^^^^^^^^
     |
     = note: `-D dead-code` implied by `-D warnings`

error: static `TIMELINE_ID_EXTRACTOR` is never used
    --> pageserver/src/tenant/timeline.rs:4276:16
     |
4276 |     pub static TIMELINE_ID_EXTRACTOR: once_cell::sync::Lazy<
     |                ^^^^^^^^^^^^^^^^^^^^^
```

A merge queue would have prevented this.

pageserver/src/tenant/timeline.rs

@@ -19,7 +19,6 @@ use tokio::sync::{oneshot, watch, Semaphore, TryAcquireError};
 use tokio_util::sync::CancellationToken;
 use tracing::*;
 use utils::id::TenantTimelineId;
-use utils::tracing_span_assert;
 
 use std::cmp::{max, min, Ordering};
 use std::collections::BinaryHeap;
@@ -4265,8 +4264,15 @@ fn rename_to_backup(path: &Path) -> anyhow::Result<()> {
     bail!("couldn't find an unused backup number for {:?}", path)
 }
 
+#[cfg(not(debug_assertions))]
+#[inline]
+pub(crate) fn debug_assert_current_span_has_tenant_and_timeline_id() {}
+
+#[cfg(debug_assertions)]
 #[inline]
 pub(crate) fn debug_assert_current_span_has_tenant_and_timeline_id() {
+    use utils::tracing_span_assert;
+
     pub static TENANT_ID_EXTRACTOR: once_cell::sync::Lazy<
         tracing_span_assert::MultiNameExtractor<2>,
     > = once_cell::sync::Lazy::new(|| {
@@ -4279,7 +4285,6 @@ pub(crate) fn debug_assert_current_span_has_tenant_and_timeline_id() {
         tracing_span_assert::MultiNameExtractor::new("TimelineId", ["timeline_id", "timeline"])
     });
 
-    #[cfg(debug_assertions)]
     match tracing_span_assert::check_fields_present([
         &*TENANT_ID_EXTRACTOR,
         &*TIMELINE_ID_EXTRACTOR,