Move private interfaces to interface extensions (#932)

macosx/InfoFileViewController.mm

@@ -8,7 +8,7 @@
 #import "FileOutlineView.h"
 #import "Torrent.h"
 
-@interface InfoFileViewController (Private)
+@interface InfoFileViewController ()
 
 - (void)setupInfo;
 
@@ -191,10 +191,6 @@
     return NSZeroRect;
 }
 
-@end
-
-@implementation InfoFileViewController (Private)
-
 - (void)setupInfo
 {
     fFileFilterField.stringValue = @"";