Simplify Sql.query_row_col function

Function `query_row` executes query and calls callback function to process
row returned. Function query_row_col() is special case, that provides
callback function, which returns value of one particular column of row,
ignoring others.

In all cases, that particular column was 0 (first and only column of
query result), since there is no point to select more than one column
with this function -- they are discarded anyway.

This commit removes that redundancy, removing column number argument of
query_row_col() function and adjusting call sites accordingly.

src/dc_receive_imf.rs

@@ -995,7 +995,6 @@ unsafe fn calc_timestamps(
             context,
             "SELECT MAX(timestamp) FROM msgs WHERE chat_id=? and from_id!=? AND timestamp>=?",
             params![chat_id as i32, from_id as i32, *sort_timestamp],
-            0,
         );
         if let Some(last_msg_time) = last_msg_time {
             if last_msg_time > 0 {