Fixed around 140 wrong namings and other refactorings which were marked as warnings

src/NadekoBot/_Extensions/Extensions.cs

@@ -112,11 +112,11 @@ public static class Extensions
         var wrap = new ReactionEventWrapper(client, msg);
         wrap.OnReactionAdded += r =>
         {
-            var _ = Task.Run(() => reactionAdded(r));
+            _= Task.Run(() => reactionAdded(r));
         };
         wrap.OnReactionRemoved += r =>
         {
-            var _ = Task.Run(() => reactionRemoved(r));
+            _= Task.Run(() => reactionRemoved(r));
         };
         return wrap;
     }

src/NadekoBot/_Extensions/StringExtensions.cs

@@ -1,6 +1,5 @@
 using NadekoBot.Common.Yml;
 using Newtonsoft.Json;
-using System.Diagnostics.CodeAnalysis;
 using System.Text;
 using System.Text.RegularExpressions;