Get rid of --ip-win32 and --route-method

[cron2]

As discussed in #239, we want to get rid of all the code path variants in the windows backend.

Since that issue was about a specific bug caused by this old cruft, I'm opening a new one that reminds us "we want this fixed, eventually".

[cron2]

Copying over the suggestions from Selva

I would suggest

- use IPAPI through iService if available
- fallback to DHCP for tap-window6 if DHCP is enabled on the adapter
    (optionally, we could continue to try enable DHCP as we do now)
- else use IPAPI or netsh directly
(optionally replace current netsh code for IPv4 with IPAPI where possible).

It would be much simpler if DHCP is completely eliminated --- no route-delay, no forking and waiting for address to
get assigned, no renew/release etc. But some setups that do not use iService may fail without it -- say, limited
privileges which is okay for DHCP. Not sure how important is that.

route-method is much easier -- just use IPAPI through iService or directly.