[foundation] Remove unused (internal) NSLogWriter (#5357)

This code was moved inside mono since it's used for `Console` output
https://github.com/mono/mono/blob/master/mcs/class/corlib/System/Console.iOS.cs

src/Foundation/NSLogWriter.cs

@@ -1,89 +0,0 @@
-//
-// Helper for Console to allow indirect access to `stdout` using NSLog
-//
-// Authors:
-//	Sebastien Pouliot  <sebastien@xamarin.com>
-//
-// Copyright 2012 Xamarin Inc. All rights reserved.
-//
-
-using System;
-using System.IO;
-using System.Runtime.InteropServices;
-using System.Text;
-
-namespace Foundation {
-
-	// this is created, by reflection, when using Console (static ctor)
-	// the linker will include this type is Console is used anywhere in the app
-	class NSLogWriter : TextWriter {
-		
-		[DllImport (Constants.FoundationLibrary)]
-		extern static void NSLog (IntPtr format, IntPtr s);
-		
-		static NSString format = new NSString ("%@");
-		
-		StringBuilder sb;
-		
-		public NSLogWriter ()
-		{
-			sb = new StringBuilder ();
-		}
-		
-		public override System.Text.Encoding Encoding {
-			get { return System.Text.Encoding.UTF8; }
-		}
-
-		public override void Flush ()
-		{
-			try {
-				using (var ns = new NSString (sb.ToString ()))
-					NSLog (format.Handle, ns.Handle);
-				sb.Length = 0;
-			}
-			catch (Exception) {
-			}
-		}
-
-		// minimum to override - see http://msdn.microsoft.com/en-us/library/system.io.textwriter.aspx
-		public override void Write (char value)
-		{
-			try {
-				sb.Append (value);
-			}
-			catch (Exception) {
-			}
-		}
-		
-		// optimization (to avoid concatening chars)
-		public override void Write (string value)
-		{
-			try {
-				sb.Append (value);
-				if (value != null && value.Length >= CoreNewLine.Length && EndsWithNewLine (value))
-					Flush ();
-			}
-			catch (Exception) {
-			}
-		}
-
-		bool EndsWithNewLine (string value)
-		{
-			for (int i = 0, v = value.Length - CoreNewLine.Length; i < CoreNewLine.Length; ++i, ++v) {
-				if (value [v] != CoreNewLine [i])
-					return false;
-			}
-
-			return true;
-		}
-		
-		public override void WriteLine ()
-		{
-			try {
-				Flush ();
-			}
-			catch (Exception) {
-			}
-		}
-	}
-}