do not SELECT timestamp if not used (#3493)

* do not `SELECT timestamp` if not used

ordering is by `id` since #2364, selecting `timestamp` is not needed.

(came over this when keeping `id` on downloading in #3487 -
had in mind there was sth. special with ids ...
however, the assumption of #2364 is even more true with #3487 -
before, new (and then maybe much larger) ids were inserted
and could result in wrong search result ordering)

* remove another unused `SELECT timestamp`

src/context.rs

@@ -594,7 +594,7 @@ impl Context {
 
         let list = if let Some(chat_id) = chat_id {
             do_query(
-                "SELECT m.id AS id, m.timestamp AS timestamp
+                "SELECT m.id AS id
                  FROM msgs m
                  LEFT JOIN contacts ct
                         ON m.from_id=ct.id
@@ -618,7 +618,7 @@ impl Context {
             // According to some tests, this limit speeds up eg. 2 character searches by factor 10.
             // The limit is documented and UI may add a hint when getting 1000 results.
             do_query(
-                "SELECT m.id AS id, m.timestamp AS timestamp
+                "SELECT m.id AS id
                  FROM msgs m
                  LEFT JOIN contacts ct
                         ON m.from_id=ct.id