V15/task/cleanup obsolete (#17433)

* Replace obsolete UserGroup Alias consts to key equivalent in tests

* Update use of usergroup alias consts to key equivalent in IsSystemgroup extension method

* Obsolete (internally) unused helper function which purpose doesn't even seem true

* Prepped EmbedProviders for proper removal of non async methods and unneeded proxy methods

* Remove obsoleted UmbracoPath and updated internal references

* Corrected  mistake and updated unittets

* Update usergroup tests that use aliases for "system" groups

* Replace more uses of globalsettings.UmbracoPath

* Remove GetDateType by key non async

* Cleanup some usages of hostingEnvironment.MapPathContentRoot

* More easy obsoletion cleanup

* Small Typeload cleanup

* More obsolete removal

* Deploy obsoletion cleanup

* Remove obsolete methods from OEmbedProviderBase.cs

---------

Co-authored-by: Zeegaan <skrivdetud@gmail.com>

src/Umbraco.Web.Common/AspNetCore/AspNetCoreBackOfficeInfo.cs

@@ -34,7 +34,7 @@ public class AspNetCoreBackOfficeInfo : IBackOfficeInfo
 
                 _getAbsoluteUrl = WebPath.Combine(
                     _hostingEnvironment.ApplicationMainUrl.ToString(),
-                    _globalSettings.CurrentValue.UmbracoPath.TrimStart(CharArrays.TildeForwardSlash));
+                    Core.Constants.System.DefaultUmbracoPath.TrimStart(CharArrays.TildeForwardSlash));
             }
 
             return _getAbsoluteUrl;