[shell] Enable sorting by default in CTRL-R

CTRL-R binding used to start with --no-sort to list the matched commands
in chronological order. However, it has been a constant source of
confusion. Let's enable it by default from now on. The sorted result
shouldn't be too confusing as we use --tiebreak=index.

test/test_go.rb

@@ -1408,6 +1408,7 @@ module TestShell
       tmux.send_keys 'C-r'
       tmux.until { |lines| lines.item_count > 0 }
     end
+    tmux.send_keys 'C-r'
     tmux.send_keys '3d'
     tmux.until { |lines| lines[-3].end_with? 'echo 3rd' }
     tmux.send_keys :Enter