R1:f8b8d8876d56

Fix call to non-existing newEmptyValue() in PhabricatorDashboardPortalProfileMenuEngine

Summary:
`PhabricatorDashboardPortalProfileMenuEngine` calls `$this->newEmptyValue()` but neither `PhabricatorDashboardPortalProfileMenuEngine` nor its parent `PhabricatorProfileMenuEngine` define a `newEmptyValue()` method.
Thus use existing `newNoContentView()` in parent `PhabricatorProfileMenuEngine` (which according to its string output is supposed to cover this case).

Test Plan:
Go to a Portal with no content.