[AppKit] Unify two partial NSLayoutManager declarations. (#14053)

One of them is empty anyway.

Also update the availability attribute for Mac Catalyst.

src/appkit.cs

@@ -22962,18 +22962,6 @@ namespace AppKit {
 			bool displayDocument, OpenDocumentCompletionHandler completionHandler);
 	}
 
-	[NoMacCatalyst]
-	partial interface NSLayoutManager {
-		// FIXME: This may need some generator work, or use IntPtr for glyphs?
-		//
-		//   ./AppKit/NSLayoutManager.g.cs(1015,44): error CS1503: Argument `#1'
-		//   cannot convert `ushort[]' expression to type `MonoMac.Foundation.NSObject[]'
-		//
-		// [Export ("showCGGlyphs:positions:count:font:matrix:attributes:inContext:")]
-		// void ShowCGGlyphs (CGGlyph [] glyphs, CGPoint [] positions, uint glyphCount, NSFont font,
-		// 	NSAffineTransform textMatrix, NSDictionary attributes, NSGraphicsContext graphicsContext);
-	}
-
 	partial interface NSViewColumnMoveEventArgs {
 		[Export ("NSOldColumn")]
 		nint OldColumn { get; }

src/xkit.cs

@@ -302,6 +302,7 @@ namespace UIKit {
 		Characters = 2,
 	}
 
+	[MacCatalyst (13,1)]
 	[NoWatch] // Header is not present in watchOS SDK.
 	[iOS (7,0)]
 	[DesignatedDefaultCtor]