Remove deprecated URL attribute alias from EventSource interface

Source/core/page/EventSource.idl

Index: Source/core/page/EventSource.idl
diff --git a/Source/core/page/EventSource.idl b/Source/core/page/EventSource.idl
index dcdc61f26676f7eeeec6cbf05e7d092e8078662e..97400c316fd7647eaf953650f8e82fa8d1ba7c5c 100644
--- a/Source/core/page/EventSource.idl
+++ b/Source/core/page/EventSource.idl
@@ -29,6 +29,8 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+// https://html.spec.whatwg.org/multipage/comms.html#the-eventsource-interface
+
 [
     ActiveDOMObject,
     Constructor(DOMString url, optional EventSourceInit eventSourceInit),
@@ -36,8 +38,6 @@
     Exposed=(Window,Worker),
     RaisesException=Constructor,
 ] interface EventSource : EventTarget {
-
-    [DeprecateAs=EventSourceURL] readonly attribute DOMString URL; // Lowercased .url is the one in the spec, but leaving .URL for compatibility reasons.
     readonly attribute DOMString url;
     readonly attribute boolean withCredentials;