package/bind: security bump to version 9.11.28

package/bind: security bump to version 9.11.28

Fixes the following security issue:

- CVE-2020-8625: When tkey-gssapi-keytab or tkey-gssapi-credential was
  configured, a specially crafted GSS-TSIG query could cause a buffer
  overflow in the ISC implementation of SPNEGO (a protocol enabling
  negotiation of the security mechanism to use for GSSAPI authentication).
  This flaw could be exploited to crash named.  Theoretically, it also
  enabled remote code execution, but achieving the latter is very difficult
  in real-world conditions

For details, see the advisory:
https://kb.isc.org/docs/cve-2020-8625

In addition, 9.11.26-27 fixed a number of issues, see the release notes for
details:
https://downloads.isc.org/isc/bind9/9.11.28/RELEASE-NOTES-bind-9.11.28.html

Drop now upstreamed patches, update the GPG key for the 2021-2022 variant
and update the COPYRIGHT hash for a change of year:

-Copyright (C) 1996-2020  Internet Systems Consortium, Inc. ("ISC")
+Copyright (C) 1996-2021  Internet Systems Consortium, Inc. ("ISC")

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>