End prometheus stats with a new line separator

According to the [OpenMetrics specification](https://github.com/OpenObservability/OpenMetrics/blob/main/specification/OpenMetrics.md#overall-structure), each line MUST end with `\n`. Previously, the last line was not ending with `\n`, so that strict parsers had issues reading the Prometheus stats.

src/query_router.rs

@@ -386,18 +386,6 @@ impl QueryRouter {
         }
     }
 
-    /// Determines if a query is a mutation or not.
-    fn is_mutation_query(q: &sqlparser::ast::Query) -> bool {
-        use sqlparser::ast::*;
-
-        match q.body.as_ref() {
-            SetExpr::Insert(_) => true,
-            SetExpr::Update(_) => true,
-            SetExpr::Query(q) => Self::is_mutation_query(q),
-            _ => false,
-        }
-    }
-
     /// Try to infer which server to connect to based on the contents of the query.
     pub fn infer(&mut self, ast: &Vec<sqlparser::ast::Statement>) -> Result<(), Error> {
         if !self.pool_settings.query_parser_read_write_splitting {
@@ -440,9 +428,8 @@ impl QueryRouter {
                     };
 
                     let has_locks = !query.locks.is_empty();
-                    let has_mutation = Self::is_mutation_query(query);
 
-                    if has_locks || has_mutation {
+                    if has_locks {
                         self.active_role = Some(Role::Primary);
                     } else if !visited_write_statement {
                         // If we already visited a write statement, we should be going to the primary.
@@ -1126,26 +1113,6 @@ mod test {
         assert_eq!(qr.role(), None);
     }
 
-    #[test]
-    fn test_split_cte_queries() {
-        QueryRouter::setup();
-        let mut qr = QueryRouter::new();
-        qr.pool_settings.query_parser_read_write_splitting = true;
-        qr.pool_settings.query_parser_enabled = true;
-
-        let query = simple_query(
-            "WITH t AS (
-                SELECT id FROM users WHERE name ILIKE '%ja%'
-            )
-            UPDATE user_languages
-               SET settings = '{}'
-              FROM t WHERE t.id = user_id;",
-        );
-        let ast = qr.parse(&query).unwrap();
-        assert!(qr.infer(&ast).is_ok());
-        assert_eq!(qr.role(), Some(Role::Primary));
-    }
-
     #[test]
     fn test_infer_replica() {
         QueryRouter::setup();