Remove unused ro.com.android.wifi-watchlist

System property ro.com.android.wifi-watchlist is automatically copied
into Settings.Secure.WIFI_WATCHDOG_WATCH_LIST which has been
deprecated and unused since API Level 16 (if not 14). Neither the
system property not its Settings.Secure counterpart is used anywhere.

This commit thus removes the automatic copying of the system property
into Settings.Secure.

Test: Device boots, Wi-Fi works
Bug: 33700679
Change-Id: If27149b863f41fed6c09b62145d5cfd96ae8e6de