Revert "[msbuild] Add forward compatibility with symlinks support (do…

…tnet#648)"

This can be reverted as we have now moved to msbuild assemblies, and
they already have this property.

This reverts commit d45f52f.

msbuild/Xamarin.MacDev.Tasks.Core/MsBuildTasks/CopyBase.cs

@@ -3,6 +3,5 @@
 	public abstract class CopyBase : Copy
 	{
 		public string SessionId { get; set; }
-		public bool UseSymboliclinksIfPossible { get; set; }		
 	}
 }