Don't dispose geometry impls.

We can't do this until we have ref counting infrastructure in, as the impls may still be in use by the deferred renderer.

src/Avalonia.Visuals/Media/Geometry.cs

@@ -131,7 +131,6 @@ namespace Avalonia.Media
         protected void InvalidateGeometry()
         {
             _isDirty = true;
-            _platformImpl?.Dispose();
             _platformImpl = null;
             Changed?.Invoke(this, EventArgs.Empty);
         }

src/Skia/Avalonia.Skia/GeometryImpl.cs

@@ -9,7 +9,6 @@ namespace Avalonia.Skia
     {
         public abstract Rect Bounds { get; }
         public abstract SKPath EffectivePath { get; }
-        public abstract void Dispose();
         public abstract bool FillContains(Point point);
         public abstract Rect GetRenderBounds(Pen pen);
         public abstract IGeometryImpl Intersect(IGeometryImpl geometry);

src/Skia/Avalonia.Skia/StreamGeometryImpl.cs

@@ -28,8 +28,6 @@ namespace Avalonia.Skia
             };
         }
 
-        public override void Dispose() => _path.Dispose();
-
         public IStreamGeometryContextImpl Open()
         {
             _path = new SKPath();

src/Skia/Avalonia.Skia/TransformedGeometryImpl.cs

@@ -23,10 +23,6 @@ namespace Avalonia.Skia
 
         public override Rect Bounds => SourceGeometry.Bounds.TransformToAABB(Transform);
 
-        public override void Dispose()
-        {
-        }
-
         public override bool FillContains(Point point)
         {
             // TODO: Not supported by SkiaSharp yet, so use expanded Rect

src/Windows/Avalonia.Direct2D1/Media/GeometryImpl.cs

@@ -23,8 +23,6 @@ namespace Avalonia.Direct2D1.Media
         /// <inheritdoc/>
         public Geometry Geometry { get; }
 
-        public void Dispose() => Geometry.Dispose();
-
         /// <inheritdoc/>
         public Rect GetRenderBounds(Avalonia.Media.Pen pen)
         {

tests/Avalonia.Visuals.UnitTests/Media/GeometryTests.cs

@@ -31,17 +31,6 @@ namespace Avalonia.Visuals.UnitTests.Media
             Assert.True(raised);
         }
 
-        [Fact]
-        public void Old_PlatformImpl_Is_Disposed_When_Updated()
-        {
-            var target = new TestGeometry();
-            var platformImpl = target.PlatformImpl;
-
-            target.Foo = true;
-
-            Mock.Get(platformImpl).Verify(x => x.Dispose());
-        }
-
         [Fact]
         public void Setting_Transform_Causes_Changed_To_Be_Raised()
         {