Avoid unnecessarily defensive IsList() checks

In both `SetCollectionValueAsync()` and `InitializeCollection`, the `IsList()` check is redundant since it has already been checked in the calling `GetParameterAsync()` or `SetPropertyAsync()` respectively. As such, there's no value in checking it _again_ since these are private methods with known entry points.

Author: JeremyCaney

OnTopic/Mapping/TopicMappingService.cs

@@ -688,13 +688,6 @@ private static bool IsList(Type targetType) =>
       \-----------------------------------------------------------------------------------------------------------------------*/
       Contract.Requires(targetType, nameof(targetType));
 
-      /*------------------------------------------------------------------------------------------------------------------------
-      | Escape clause if preconditions are not met
-      \-----------------------------------------------------------------------------------------------------------------------*/
-      if (!IsList(targetType)) {
-        return (IList?)null;
-      }
-
       /*------------------------------------------------------------------------------------------------------------------------
       | Attempt to create specific type
       \-----------------------------------------------------------------------------------------------------------------------*/
@@ -763,11 +756,6 @@ MappedTopicCache          cache
       Contract.Requires(configuration, nameof(configuration));
       Contract.Requires(cache, nameof(cache));
 
-      /*------------------------------------------------------------------------------------------------------------------------
-      | Escape clause if preconditions are not met
-      \-----------------------------------------------------------------------------------------------------------------------*/
-      if (!IsList(configuration.Property.PropertyType)) return;
-
       /*------------------------------------------------------------------------------------------------------------------------
       | Ensure target list is created
       \-----------------------------------------------------------------------------------------------------------------------*/