Make RuntimeResult abstract

It never really made sense to have it instantiable in the first place,
frankly.

src/Discord.Net.Commands/Results/RuntimeResult.cs

@@ -6,7 +6,7 @@ using System.Text;
 namespace Discord.Commands
 {
     [DebuggerDisplay(@"{DebuggerDisplay,nq}")]
-    public class RuntimeResult : IResult
+    public abstract class RuntimeResult : IResult
     {
         protected RuntimeResult(CommandError? error, string reason)
         {
@@ -21,13 +21,6 @@ namespace Discord.Commands
 
         string IResult.ErrorReason => Reason;
 
-        public static RuntimeResult FromSuccess(string reason = null) =>
-            new RuntimeResult(null, reason);
-        public static RuntimeResult FromError(string reason) =>
-            new RuntimeResult(CommandError.Unsuccessful, reason);
-        public static RuntimeResult FromError(IResult result) =>
-            new RuntimeResult(result.Error, result.ErrorReason);
-
         public override string ToString() => Reason ?? (IsSuccess ? "Successful" : "Unsuccessful");
         private string DebuggerDisplay => IsSuccess ? $"Success: {Reason ?? "No Reason"}" : $"{Error}: {Reason}";
     }