code_style: remove deprecated UseMicaOnWindows11

Signed-off-by: leo <longshuang@msn.cn>

Author: love-linger

src/Models/ThemeOverrides.cs

@@ -1,5 +1,4 @@
 using System.Collections.Generic;
-
 using Avalonia.Media;
 
 namespace SourceGit.Models
@@ -9,7 +8,6 @@ public class ThemeOverrides
         public Dictionary<string, Color> BasicColors { get; set; } = new Dictionary<string, Color>();
         public double GraphPenThickness { get; set; } = 2;
         public double OpacityForNotMergedCommits { get; set; } = 0.5;
-        public bool UseMicaOnWindows11 { get; set; } = true;
         public List<Color> GraphColors { get; set; } = new List<Color>();
     }
 }