ipn/ipnlocal: remove windows exception from profile migration

The check in question results in profiles never being migrated to backend
prefs on Windows clients. We should be doing that on Windows too.

This should be save vis-a-vis unattended mode since we won't see the
unmigrated prefs until the GUI signs in.

Fixes #7398

Signed-off-by: Aaron Klotz <aaron@tailscale.com>

ipn/ipnlocal/profiles.go

@@ -534,7 +534,7 @@ func newProfileManagerWithGOOS(store ipn.StateStore, logf logger.Logf, goos stri
 		if err := pm.setPrefsLocked(prefs); err != nil {
 			return nil, err
 		}
-	} else if len(knownProfiles) == 0 && goos != "windows" {
+	} else if len(knownProfiles) == 0 {
 		// No known profiles, try a migration.
 		if err := pm.migrateFromLegacyPrefs(); err != nil {
 			return nil, err