lib/bourne-shell.sh: Don't force-load bash-completion

Its already done better by the "system" completion module, and doing it
there too makes disabling it impossible and debgging issues harder.

lib/bourne-shell.sh

@@ -98,14 +98,3 @@ fi
 if [ -f ~/.bashrc.local ]; then
     . ~/.bashrc.local
 fi
-
-# enable programmable completion features (you don't need to enable
-# this, if it's already enabled in /etc/bash.bashrc and /etc/profile
-# sources /etc/bash.bashrc).
-if ! shopt -oq posix; then
-  if [ -f /usr/share/bash-completion/bash_completion ]; then
-    . /usr/share/bash-completion/bash_completion
-  elif [ -f /etc/bash_completion ]; then
-    . /etc/bash_completion
-  fi
-fi