end_entity: fix dns_names rustdoc comment

Prior to this commit the rustdoc comment on `EndEntityCert.dns_names`
mentioned using `verify_is_valid_for_dns_name` and
`verify_is_valid_for_at_least_one_dns_name`, but these functions don't
exist anymore.

This commit updates the comment to point to
`EndEntityCert::verify_is_valid_for_subject_name`, and does so with
a proper Rustdoc link so that future updates will be caught by `cargo
doc` if we forget to fix this reference to match.

Author: cpu

src/end_entity.rs

@@ -154,8 +154,8 @@ impl<'a> EndEntityCert<'a> {
     /// extension. Invalid names are skipped.
     ///
     /// This function must not be used to implement custom DNS name verification.
-    /// Verification functions are already provided as `verify_is_valid_for_dns_name`
-    /// and `verify_is_valid_for_at_least_one_dns_name`.
+    /// Checking that a certificate is valid for a given subject name should always be done with
+    /// [EndEntityCert::verify_is_valid_for_subject_name].
     #[cfg(feature = "alloc")]
     pub fn dns_names(&'a self) -> impl Iterator<Item = GeneralDnsNameRef<'a>> {
         subject_name::list_cert_dns_names(self)