[introspection] Don't check native signatures on obsolete members, and ignore the right simd matrix types.

Fixes this introspection/Mac problem:

    ***** ApiSignatureTest.NativeSignatures
    Selector: uniformWithName:matrixFloat2x2: on type SpriteKit.SKUniform, Type: Simd.MatrixFloat2x2, nothing encoded
    Selector: uniformWithName:matrixFloat3x3: on type SpriteKit.SKUniform, Type: Simd.MatrixFloat3x3, nothing encoded
    Selector: uniformWithName:matrixFloat4x4: on type SpriteKit.SKUniform, Type: Simd.MatrixFloat4x4, nothing encoded
    Selector: setMatrixFloat2x2Value: on type SpriteKit.SKUniform, Type: Simd.MatrixFloat2x2, nothing encoded
    Selector: setMatrixFloat3x3Value: on type SpriteKit.SKUniform, Type: Simd.MatrixFloat3x3, nothing encoded
    Selector: setMatrixFloat4x4Value: on type SpriteKit.SKUniform, Type: Simd.MatrixFloat4x4, nothing encoded
    Selector: initWithName:matrixFloat2x2: on type SpriteKit.SKUniform, Type: Simd.MatrixFloat2x2, nothing encoded
    Selector: initWithName:matrixFloat3x3: on type SpriteKit.SKUniform, Type: Simd.MatrixFloat3x3, nothing encoded
    Selector: initWithName:matrixFloat4x4: on type SpriteKit.SKUniform, Type: Simd.MatrixFloat4x4, nothing encoded

tests/introspection/ApiSignatureTest.cs

@@ -233,6 +233,10 @@ namespace Introspection {
 			if (methodinfo == null && constructorinfo == null)
 				return;
 
+			// Don't check obsolete methods, it could be obsoleted because it was broken.
+			if (m.GetCustomAttributes<ObsoleteAttribute> () != null)
+				return;
+			
 			if (m.DeclaringType != t)
 				return;
 			
@@ -388,9 +392,9 @@ namespace Introspection {
 			case "Vector4":
 			case "Vector4i":
 			case "Vector4d":
-			case "Matrix2":
-			case "Matrix3":
-			case "Matrix4":
+			case "MatrixFloat2x2":
+			case "MatrixFloat3x3":
+			case "MatrixFloat4x4":
 			case "MDLAxisAlignedBoundingBox": // struct { Vector3, Vector3 }
 				return true;
 			default: