Use simplesamlphp from debian packages rather than installing via ansible

[frankduncan]

Currently we manually install simplesamlphp in the ansible code. The tar is actually in this repository under thirdparty. This is not easy for sysadmins to maintain as it adds one more thing to check for every machine when security updates are released.

So update the ansible config to install via debian. The catch is that we modify simplesamlphp a bit to enable okta and disable the web interface. Those things would need to survive updates to the debian package, so that all needs to be rectified.