Delete ignore! macro

This was a holdover from when we didn't allow nested comment blocks
(think #if 0). It isn't used anywhere.

Author: sfackler

src/libstd/macros.rs

@@ -9,9 +9,6 @@
 // except according to those terms.
 #[macro_escape];
 
-#[macro_export]
-macro_rules! ignore (($($x:tt)*) => (()))
-
 #[macro_export]
 macro_rules! log(
     ($lvl:expr, $($arg:tt)+) => ({