Revert "zsh: profile-relative functions path"

This reverts commit 766207ca1d52db37df5ca17b9bd3bd21a03dfafd.

We need to solve the problem with `environment.profileRelativeEnvVars`.
The best workaround is to make profileRelativeEnvVars prepend paths.

nixos/modules/programs/zsh/zsh.nix

···
 
     };
 
-    environment.profileRelativeEnvVars =
-      { FPATH = [ "/share/zsh/site-functions" ];
-      };
-
     environment.etc."zshenv".text =
       ''
         # /etc/zshenv: DO NOT EDIT -- this file has been generated automatically.