libmpdclient: create alias

Alias mpd_clientlib to libmpdclient.

pkgs/top-level/aliases.nix

···
   mono-zeroconf = throw "mono-zeroconf was deprecated on 2019-09-20: abandoned by upstream.";
   mozart = mozart2-binary; # added 2019-09-23
   mozart-binary = mozart2-binary; # added 2019-09-23
+  mpd_clientlib = libmpdclient; # added 2021-02-11
   mpich2 = mpich;  # added 2018-08-06
   msf = metasploit; # added 2018-04-25
   libmsgpack = msgpack; # added 2018-08-17

pkgs/top-level/all-packages.nix

···
   inherit (callPackages ../servers/mpd { })
     mpd mpd-small mpdWithFeatures;
 
-  mpd_clientlib = libmpdclient;
   libmpdclient = callPackage ../servers/mpd/libmpdclient.nix { };
 
   mpdscribble = callPackage ../tools/misc/mpdscribble { };