remove unneeded 'mut'

example/fuzzy-pickles/src/main.rs

@@ -14,7 +14,7 @@ pub fn main() {
 
     let mut buf = String::new();
     {
-        let mut buf_bytes = unsafe { buf.as_mut_vec() };
+        let buf_bytes = unsafe { buf.as_mut_vec() };
         for idx in 0..data.len() {
             buf_bytes.push(data[idx]);
         }