Remove redundant reserve call (#674)

src/bytes_mut.rs

@@ -1283,9 +1283,7 @@ impl Extend<u8> for BytesMut {
 
         // TODO: optimize
         // 1. If self.kind() == KIND_VEC, use Vec::extend
-        // 2. Make `reserve` inline-able
         for b in iter {
-            self.reserve(1);
             self.put_u8(b);
         }
     }