pageserver: demote range end fallback log (#7403)

## Problem
This trace is emitted whenever a vectored read touches the end of a
delta layer file. It's a perfectly normal case, but I expected it to be
more rare when implementing the code.

## Summary of changes
Demote log to debug.

pageserver/src/tenant/storage_layer/delta_layer.rs

@@ -939,7 +939,7 @@ impl DeltaLayerInner {
             }
 
             if !range_end_handled {
-                tracing::info!("Handling range end fallback at {}", data_end_offset);
+                tracing::debug!("Handling range end fallback at {}", data_end_offset);
                 planner.handle_range_end(data_end_offset);
             }
         }