Updating MonoGame-specific offset as it's not required anymore.

src/ImGui.NET.SampleProgram.XNA/ImGuiRenderer.cs

@@ -195,17 +195,9 @@ namespace ImGuiNET.SampleProgram.XNA
 
             var io = ImGui.GetIO();
 
-            // MonoGame-specific //////////////////////
-            var offset = .5f;
-            ///////////////////////////////////////////
-
-            // FNA-specific ///////////////////////////
-            //var offset = 0f;
-            ///////////////////////////////////////////
-
             _effect.World = Matrix.Identity;
             _effect.View = Matrix.Identity;
-            _effect.Projection = Matrix.CreateOrthographicOffCenter(offset, io.DisplaySize.X + offset, io.DisplaySize.Y + offset, offset, -1f, 1f);
+            _effect.Projection = Matrix.CreateOrthographicOffCenter(0f, io.DisplaySize.X, io.DisplaySize.Y, 0f, -1f, 1f);
             _effect.TextureEnabled = true;
             _effect.Texture = texture;
             _effect.VertexColorEnabled = true;