Revert "feat: implement IntoIter for owned body"

An iterator that consumes Body needs to hold on to its arena, see
discussion in #6.

This reverts commit 8b82c43.

src/body.rs

@@ -188,11 +188,3 @@ impl<'a> IntoIterator for &'a Body<'a> {
         self.elems.iter()
     }
 }
-
-impl<'a> IntoIterator for Body<'a> {
-    type Item = (Key, Value<'a>);
-    type IntoIter = std::vec::IntoIter<(Key, Value<'a>)>;
-    fn into_iter(self) -> Self::IntoIter {
-        self.elems.into_iter()
-    }
-}