chore(deps): drop the unused Avalonia.Themes.Fluent package

The app styles itself with Semi.Avalonia only; nothing references the
Fluent theme.

YKanBan/YKanBan.csproj

@@ -39,7 +39,6 @@
   <ItemGroup>
     <PackageReference Include="Avalonia" Version="11.3.22" />
     <PackageReference Include="Avalonia.Desktop" Version="11.3.22" />
-    <PackageReference Include="Avalonia.Themes.Fluent" Version="11.3.22" />
     <PackageReference Include="Avalonia.Fonts.Inter" Version="11.3.22" />
     <!--Condition below is needed to remove Avalonia.Diagnostics package from build output in Release configuration.-->
     <PackageReference Include="Avalonia.Diagnostics" Version="11.3.22">