Fixed SoundEffectInstance looping under XAudio (MonoGame#8748)

Fixed SoundEffectInstance looping under XAudio as reported in
MonoGame#8711.

Author: tomspilman

MonoGame.Framework/Platform/Audio/SoundEffectInstance.XAudio.cs

@@ -24,7 +24,6 @@ public partial class SoundEffectInstance : IDisposable
         private float _reverbMix;
 
         private bool _paused;
-        private bool _loop;
 
         private void PlatformInitialize(byte[] buffer, int sampleRate, int channels)
         {
@@ -162,7 +161,7 @@ private void PlatformPlay()
             if (_voice != null && SoundEffect.MasterVoice != null)
             {
                 // Choose the correct buffer depending on if we are looped.            
-                var buffer = _loop ? _effect._loopedBuffer : _effect._buffer;
+                var buffer = _isLooped ? _effect._loopedBuffer : _effect._buffer;
 
                 if (_voice.State.BuffersQueued > 0)
                 {
@@ -182,7 +181,7 @@ private void PlatformResume()
             if (_voice != null && SoundEffect.MasterVoice != null)
             {
                 // Restart the sound if (and only if) it stopped playing
-                if (!_loop)
+                if (!_isLooped)
                 {
                     if (_voice.State.BuffersQueued == 0)
                     {
@@ -207,7 +206,7 @@ private void PlatformStop(bool immediate)
                 }
                 else
                 {
-                    if (_loop)
+                    if (_isLooped)
                         _voice.ExitLoop();
                     else
                         _voice.Stop((int)PlayFlags.Tails);
@@ -217,16 +216,6 @@ private void PlatformStop(bool immediate)
             _paused = false;
         }
 
-        private void PlatformSetIsLooped(bool value)
-        {
-            _loop = value;
-        }
-
-        private bool PlatformGetIsLooped()
-        {
-            return _loop;
-        }
-
         private void PlatformSetPan(float value)
         {
             // According to XNA documentation: