style: remove eprintln macro

The eprintln! macro was added to Rust's standard library in Rust 1.19.0,
which is below ripgrep's minimum Rust version. Therefore, we can rely on
the standard library variant now.

src/main.rs

@@ -35,13 +35,6 @@ macro_rules! errored {
     }
 }
 
-macro_rules! eprintln {
-    ($($tt:tt)*) => {{
-        use std::io::Write;
-        let _ = writeln!(&mut ::std::io::stderr(), $($tt)*);
-    }}
-}
-
 mod app;
 mod args;
 mod decoder;