No longer try installing Python grip package (#354)

As of 2020-May-09, and probably some months earlier, attempting to
install the Python 'grip' package fails on Ubuntu 16.04 systems.  This
package is not essential for using the P4 open source development
tools.

vm/user-bootstrap.sh

@@ -117,8 +117,6 @@ sudo pip install crcmod
 git clone https://github.com/p4lang/tutorials
 sudo mv tutorials /home/p4
 sudo chown -R p4:p4 /home/p4/tutorials
-# Install grip for offline markdown rendering
-sudo pip install grip
 
 # --- Emacs --- #
 sudo cp p4_16-mode.el /usr/share/emacs/site-lisp/