detach_ancestor: delete the right layer when hardlink fails (#12397)

If a hardlink operation inside `detach_ancestor` fails due to the layer
already existing, we delete the layer to make sure the source is one we
know about, and then retry.

But we deleted the wrong file, namely, the one we wanted to use as the
source of the hardlink. As a result, the follow up hard link operation
failed. Our PR corrects this mistake.

pageserver/src/tenant/timeline/detach_ancestor.rs

@@ -885,7 +885,7 @@ async fn remote_copy(
                 }
                 tracing::info!("Deleting orphan layer file to make way for hard linking");
                 // Delete orphan layer file and try again, to ensure this layer has a well understood source
-                std::fs::remove_file(adopted_path)
+                std::fs::remove_file(&adoptee_path)
                     .map_err(|e| Error::launder(e.into(), Error::Prepare))?;
                 std::fs::hard_link(adopted_path, &adoptee_path)
                     .map_err(|e| Error::launder(e.into(), Error::Prepare))?;