Remove the secure lock icon from the status bar.

Added in I0e08a952904cc4728621953a42806edf26eb8e46, but
takes up too much room.

An undocumented system setting, "show_status_bar_lock", can
be set to 1 (e.g. in Spare Parts) to bring this back.

Bug: 2511090
Change-Id: I8869ac18c303a786eeb7f1a0c4ae08529b45d59c