Remove test of error message that can vary between MongoDB versions

tests/cursor.rs

@@ -53,10 +53,6 @@ fn test_tailing_cursor() {
     let failing_cursor = normal_collection.tail(doc!{}, None, None);
     let failing_result = failing_cursor.into_iter().next().unwrap();
     assert!(failing_result.is_err());
-    assert_eq!(
-        "MongoError (BsoncError: Query/Unknown - Unable to execute query: error processing query: ns=rust_test.not_capped limit=0 skip=0\nTree: $and\nSort: {}\nProj: {}\n tailable cursor requested on non capped collection)",
-        format!("{:?}", failing_result.err().unwrap())
-    );
 
     let document = doc! { "key_1" => "Value 1" };
     // Insert a first document into the collection