Removes more old backoffice files + Smidge! (#15788)

* Removes lots of files used by the old backoffice and that is not needed for the management api

* A little clean-up

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Co-authored-by: kjac <kja@umbraco.dk>

tests/Umbraco.Tests.Integration/Testing/UmbracoIntegrationTest.cs

@@ -150,7 +150,6 @@ public abstract class UmbracoIntegrationTest : UmbracoIntegrationTestBase
         builder.AddConfiguration()
             .AddUmbracoCore()
             .AddWebComponents()
-            .AddRuntimeMinifier()
             .AddBackOfficeAuthentication()
             .AddBackOfficeIdentity()
             .AddMembersIdentity()