[web] Don't add href="#" to semantics links (flutter/engine#53395)

This is a stopgap for issues like https://github.com/flutter/flutter/issues/146291 until we land better link semantics (in https://github.com/flutter/flutter/issues/150263 and https://github.com/flutter/packages/pull/6711). For the time being, the `href="#"` isn't providing any extra value, and is causing the browser to navigate to to `#` whenever the semantics link is clicked, which is undesirable.

Fixes https://github.com/flutter/flutter/issues/146291

engine/src/flutter/lib/web_ui/lib/src/engine/semantics/link.dart

@@ -18,9 +18,8 @@ class Link extends PrimaryRoleManager {
   @override
   DomElement createElement() {
     final DomElement element = domDocument.createElement('a');
-    // TODO(chunhtai): Fill in the real link once the framework sends entire uri.
-    // https://github.com/flutter/flutter/issues/102535.
-    element.setAttribute('href', '#');
+    // TODO(mdebbar): Fill in the real link once the framework sends entire uri.
+    // https://github.com/flutter/flutter/issues/150263.
     element.style.display = 'block';
     return element;
   }

engine/src/flutter/lib/web_ui/test/engine/semantics/semantics_test.dart

@@ -3536,6 +3536,7 @@ void _testLink() {
 
     final SemanticsObject object = pumpSemantics();
     expect(object.element.tagName.toLowerCase(), 'a');
+    expect(object.element.hasAttribute('href'), isFalse);
   });
 }