{mcaimi-,x,}st: move to pkgs/by-name

pkgs/top-level/all-packages.nix

···
     emojiSupport = true;
   };
 
-  st = callPackage ../applications/terminal-emulators/st { };
-  xst = callPackage ../applications/terminal-emulators/st/xst.nix { };
-  mcaimi-st = callPackage ../applications/terminal-emulators/st/mcaimi-st.nix { };
-
   termite = callPackage ../applications/terminal-emulators/termite/wrapper.nix {
     termite = termite-unwrapped;
   };