places: Remove the transaction from fetch_tree_with_depth.

Originally, we used multiple SELECTs to populate the tree, and needed
the read-only transaction to avoid interleaved writes. The multiple
SELECTs were removed in mozilla#1289, so the transaction (1) isn't needed
anymore, and (2) causes issues when calling `fetch_tree_with_depth`
concurrently.

Closes mozilla#5773.

CHANGELOG.md

@@ -2,6 +2,12 @@
 
 [Full Changelog](In progress)
 
+## Places
+
+### 🦊 What's Changed 🦊
+
+- `fetch_tree_with_depth` no longer starts a transaction when reading from the database. The transaction causes issues with concurrent calls, and isn't needed for consistency anymore ([#5790](https://github.com/mozilla/application-services/pull/5790)).
+
 # v118.0 (_2023-08-28_)
 
 ## General

components/places/src/storage/bookmarks/fetch.rs

@@ -226,7 +226,6 @@ pub fn fetch_tree_with_depth(
     item_guid: &SyncGuid,
     target_depth: &FetchDepth,
 ) -> Result<Option<Item>> {
-    let _tx = db.begin_transaction()?;
     let (tree, parent_guid, position) = if let Some((tree, parent_guid, position)) =
         json_tree::fetch_tree(db, item_guid, target_depth)?
     {