Find and delete the registry keys for the unwanted networks under these locations:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\NetworkList\Nla\Cache\Intranet
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\NetworkList\Profiles
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\NetworkList\Signatures\Unmanaged

If you don’t mind reconfiguring any existing networks, its easiest to disable your network adapter, delete all the networks, then re-enable.

Note: The known networks described above are separate from wireless user profiles, which store SSIDs, WPA2 passwords, etc. The UI for managing wireless user profiles is also gone. These can be wiped clean by removing the wireless adapter from Device Manager (Windows will restore it fresh) or removed individually with netsh wlan delete profile “profile name