labwc: migrate to by-name

pkgs/top-level/all-packages.nix

···
 
   lame = callPackage ../development/libraries/lame { };
 
-  labwc = callPackage ../applications/window-managers/labwc {
+  labwc = callPackage ../by-name/la/labwc/package.nix {
     wlroots = wlroots_0_16;
   };