Move the ipn/desktop blank import from cmd/tailscaled/tailscaled_windows.go
into feature/condregister/maybe_desktop_sessions.go, consistent with how
all other modular features are registered. tailscaled already imports
feature/condregister, so it still gets ipn/desktop on Windows.
Updates #12614
Change-Id: I92418c4bf0e67f0ab40542e47584762ac0ffa2b2
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>