Implement deletion of sl alias as per #3055

lib/directories.zsh

@@ -27,7 +27,6 @@ alias lsa='ls -lah'
 alias l='ls -la'
 alias ll='ls -l'
 alias la='ls -lA'
-alias sl=ls # often screw this up
 
 # Push and pop directories on directory stack
 alias pu='pushd'