Simplify Shiny SID creation

calculates a passing SID and applies random bits to not be too
predictable
no need to bruteforce

PKHeX.Core/PKM/PKM.cs

@@ -772,7 +772,8 @@ public void setShinyPID()
         public void setShinySID()
         {
             if (IsShiny) return;
-            do SID = Util.rnd16(); while (!IsShiny);
+            var xor = TID ^ (PID >> 16) ^ (PID & 0xFFFF);
+            SID = (int)((xor & 0xFFF8) | (Util.rnd32() & 7));
         }
         /// <summary>
         /// Applies a PID to the <see cref="PKM"/> according to the specified <see cref="Gender"/>.

PKHeX.Core/Util/RandUtil.cs

@@ -9,10 +9,6 @@ public static uint rnd32()
         {
             return (uint)rand.Next(1 << 30) << 2 | (uint)rand.Next(1 << 2);
         }
-        internal static ushort rnd16()
-        {
-            return (ushort)rand.Next(ushort.MaxValue);
-        }
         public static void Shuffle<T>(T[] array)
         {
             int n = array.Length;

PKHeX.WinForms/Controls/PKM Editor/PKMEditor.cs

@@ -1487,7 +1487,7 @@ private void updateShiny(bool PID)
 
             if (pkm.Format > 2)
             { 
-                if(PID)
+                if (PID)
                 {
                     pkm.setShinyPID();
                     TB_PID.Text = pkm.PID.ToString("X8");