Update atkmm1_6 to version 2.28.3 / rev 8 via SR 1155247
https://build.opensuse.org/request/show/1155247
by user dimstar + dimstar_suse
- Drop baselibs.conf: the -32bit packages are no longer needed and
have not been part of Tumbleweed for a while already (build for
i586 only enabled in LegacyX86). (forwarded request 1155231 from dimstar)