Get rid of virtualbox, and also unused packer files. (#85)

## Summary:
The packer files were an experiment that has been dropped.  And we
haven't used virtualbox in a long time -- we don't even install it on
mac anymore.  So let's not install it on linux either (it's big).

Issue: none

## Test plan:
Fingers crossed

Author: csilvers

Reviewers: daelious, yogieric

Required Reviewers:

Approved By: daelious

Checks:

Pull Request URL: #85

bin/install-mac-apps.sh

@@ -55,8 +55,6 @@ install_mac_apps() {
     firefox firefox-developer-edition google-chrome google-chrome-canary
     # Tools
     dropbox google-drive-file-stream iterm2 zoomus
-    # Virtualbox (requires difficult meraki workaround in Catalina++)
-    #virtualbox
     # Text Editors
     macvim sublime-text textmate atom
     # Chat

linux-functions.sh

@@ -173,7 +173,7 @@ EOF
     sudo npm install -g yarn
 
     # Not technically needed to develop at Khan, but we assume you have it.
-    sudo apt-get install -y unrar virtualbox ack-grep
+    sudo apt-get install -y unrar ack-grep
 
     # Not needed for Khan, but useful things to have.
     sudo apt-get install -y ntp abiword curl diffstat expect gimp \

linux-setup.sh

@@ -244,7 +244,7 @@ EOF
     sudo npm install -g [email protected]
 
     # Not technically needed to develop at Khan, but we assume you have it.
-    sudo apt-get install -y unrar virtualbox ack-grep
+    sudo apt-get install -y unrar ack-grep
 
     # Not needed for Khan, but useful things to have.
     sudo apt-get install -y ntp abiword diffstat expect gimp \