IDL test: Remove title argument for registerProtocolHandler()

This was discussed in [1] and test added in [2]. This commit updates
the corresponding IDL test.

[1] whatwg/html#5425
[2] #22678

interfaces/html.idl

@@ -1969,7 +1969,7 @@ interface mixin NavigatorLanguage {
 };
 
 interface mixin NavigatorContentUtils {
-  [SecureContext] void registerProtocolHandler(DOMString scheme, USVString url, DOMString title);
+  [SecureContext] void registerProtocolHandler(DOMString scheme, USVString url);
   [SecureContext] void unregisterProtocolHandler(DOMString scheme, USVString url);
 };