Move naive_bytecount to pedantic

As discussed on Zulip, current best practice is to avoid recommending
external crates. This lint is from before that was enforced. Move it
to the pedantic group to avoid enabling it by default.

https://rust-lang.zulipchat.com/#narrow/stream/257328-clippy/topic/naive_bytecount.20suggesting.20extra.20dependency

clippy_lints/src/bytecount.rs

@@ -28,7 +28,7 @@ declare_clippy_lint! {
     /// &vec.iter().filter(|x| **x == 0u8).count(); // use bytecount::count instead
     /// ```
     pub NAIVE_BYTECOUNT,
-    perf,
+    pedantic,
     "use of naive `<slice>.filter(|&x| x == y).count()` to count byte values"
 }