paths: add missing js/wasm stub

Change-Id: Iae4838f5fa1dc0cd491d5a3ac906fd3cdacb173c
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

paths/paths_js.go

@@ -7,3 +7,5 @@ package paths
 func ensureStateDirPerms(dirPath string) error {
 	return nil
 }
+
+func LegacyStateFilePath() string { return "" }