Revert "わざと警告を発生させる"

This reverts commit 9dfb9d7.

Author: laysakura

chapter2/src/2_8_1/main.rs

@@ -34,8 +34,6 @@ fn write_fmt<W: fmt::Write>(w: &mut W) {
 }
 
 fn main() -> io::Result<()> {
-    let x = 42;
-
     let tmp_path = mktemp();
     {
         let mut contents = String::new();