[Wi-Fi] Remove $ icon for metered Wi-Fi networks

It has some problems:
1. The $ icon does not disappear right after set unmetered.
2. Security icon is at the same position and it takes higher priority than
    the $ icon. It's not a consistent UX since $ icon is only for open network.
3. No localization design for the $ icon.

Bug: 150912127
Test: Manual
      In Wi-Fi picker, check if $ icon is visible on metered Wi-Fi networks.
Change-Id: Ia929bbaa65367fe6f3bfba7fdd924c23622ca3ca