fix reference to nonexistent field

It's not really needed anyway, since managed threads will end when SMAPI exits.

src/SMAPI/Framework/SCore.cs

@@ -282,7 +282,6 @@ namespace StardewModdingAPI.Framework
                 {
                     if (this.IsGameRunning)
                     {
-                        this.inputThread.Abort();
                         this.LogManager.WriteCrashLog();
                         this.Game.Exit();
                     }