Removed legacy suppressions from Microsoft Code Contracts

Microsoft Code Contract's static code analysis was prone to a number of false positives, which necessitated a few `[SuppressMessage()]` attributes to be sprinkled in the code. Since we no longer use Microsoft Code Contracts—and, in fact, the static code analysis isn't even supported with .NET Standard!—we're removing these suppressions.

Author: JeremyCaney

OnTopic.Data.Caching/CachedTopicRepository.cs

@@ -142,11 +142,6 @@ public override int Save(Topic topic, bool isRecursive = false, bool isDraft = f
     | METHOD: MOVE
     \-------------------------------------------------------------------------------------------------------------------------*/
     /// <inheritdoc />
-    [System.Diagnostics.CodeAnalysis.SuppressMessage(
-      "Microsoft.Contracts",
-      "TestAlwaysEvaluatingToAConstant",
-      Justification = "Sibling may be null from overloaded caller."
-      )]
     public override void Move(Topic topic, Topic target, Topic? sibling) => _dataProvider.Move(topic, target, sibling);
 
     /*==========================================================================================================================

OnTopic.Data.Sql/SqlTopicRepository.cs

@@ -517,11 +517,6 @@ void recurse() {
     | METHOD: MOVE
     \-------------------------------------------------------------------------------------------------------------------------*/
     /// <inheritdoc />
-    [System.Diagnostics.CodeAnalysis.SuppressMessage(
-      "Microsoft.Contracts",
-      "TestAlwaysEvaluatingToAConstant",
-      Justification = "Sibling may be null from overloaded caller."
-      )]
     public override void Move(Topic topic, Topic target, Topic? sibling) {
 
       /*------------------------------------------------------------------------------------------------------------------------

OnTopic.TestDoubles/StubTopicRepository.cs

@@ -139,11 +139,6 @@ public override int Save(Topic topic, bool isRecursive = false, bool isDraft = f
     | METHOD: MOVE
     \-------------------------------------------------------------------------------------------------------------------------*/
     /// <inheritdoc />
-    [System.Diagnostics.CodeAnalysis.SuppressMessage(
-      "Microsoft.Contracts",
-      "TestAlwaysEvaluatingToAConstant",
-      Justification = "Sibling may be null from overloaded caller."
-      )]
     public override void Move(Topic topic, Topic target, Topic? sibling) {
 
       /*------------------------------------------------------------------------------------------------------------------------