Remove workaround for markup stripping dartdoc bug (flutter#20748)

* Remove workaround for dart-lang/dartdoc#1125

* Update update_icons.dart for optional const and to remove markup stripping workaround

Author: jcollins-g

dev/tools/update_icons.dart

@@ -216,7 +216,7 @@ String getIconDeclaration(String line) {
   final String rtl = kMirroredIcons.contains(name) ? ', matchTextDirection: true' : '';
   return '''
 
-  /// <p><i class="material-icons md-36">$name</i> &#x2014; material icon named "$description".</p>
-  static const IconData $identifier = const IconData(0x$codepoint, fontFamily: 'MaterialIcons'$rtl);
+  /// <i class="material-icons md-36">$name</i> &#x2014; material icon named "$description".
+  static const IconData $identifier = IconData(0x$codepoint, fontFamily: 'MaterialIcons'$rtl);
 ''';
 }