Fix/mute code style warnings

Common.ruleset

@@ -461,6 +461,10 @@
 		<!-- Use the Regex source generator -->
 		<Rule Id="MA0110" Action="Error" />
 	</Rules>
+	<Rules AnalyzerId="Microsoft.CodeAnalysis.FxCopAnalyzers" RuleNamespace="Microsoft.CodeAnalysis.FxCopAnalyzers">
+		<!-- Implement serialization constructors -->
+		<Rule Id="CA2229" Action="Hidden" />
+	</Rules>
 	<Rules AnalyzerId="StyleCop.Analyzers" RuleNamespace="StyleCop.Analyzers.SpacingRules">
 		<!-- Keywords should be spaced correctly -->
 		<Rule Id="SA1000" Action="Hidden" />

src/BizHawk.Common/Win32/RawInputImports.cs

@@ -1,6 +1,4 @@
-#nullable enable
-
-using System;
+using System;
 using System.Runtime.InteropServices;
 
 // ReSharper disable FieldCanBeMadeReadOnly.Global

src/BizHawk.Common/macOS/QuartzImports.cs

@@ -1,6 +1,4 @@
-#nullable enable
-
-using System.Runtime.InteropServices;
+using System.Runtime.InteropServices;
 
 namespace BizHawk.Common
 {