Drop the '2' suffix from logging macros

Who doesn't like a massive renaming?

src/test/run-pass/string-self-append.rs

@@ -16,7 +16,7 @@ pub fn main() {
     let mut i = 20;
     let mut expected_len = 1u;
     while i > 0 {
-        error2!("{}", a.len());
+        error!("{}", a.len());
         assert_eq!(a.len(), expected_len);
         a = a + a; // FIXME(#3387)---can't write a += a
         i -= 1;