encoding: remove redundant pointer cast in url::percent_decode_utf8

A debug assertion in `encoding::url::percent_decode_utf8` previously
cast the result of `[u8]::as_ptr` to `*const u8`, which was redundant
because the return type of the `as_ptr` call was already `*const u8`.
This patch removes the redundant cast.

src/encoding/url.rs

@@ -396,7 +396,7 @@ where
             Cow::Borrowed(decoded_str) => {
                 debug_assert_eq!(decoded_str.len(), decoded.len());
                 debug_assert_eq!(
-                    decoded_str.as_bytes().as_ptr() as *const u8,
+                    decoded_str.as_bytes().as_ptr(),
                     decoded.as_ptr()
                 );