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/TestServerTest/UmbracoTestServerTestBase.cs

@@ -249,7 +249,6 @@ namespace Umbraco.Cms.Tests.Integration.TestServerTest
                 .AddUmbracoCore()
                 .AddWebComponents()
                 .AddNuCache()
-                .AddRuntimeMinifier()
                 .AddBackOfficeCore()
                 .AddBackOfficeAuthentication()
                 .AddBackOfficeIdentity()