Revert "Add botan 2 support"

This change adds a mandatory dependency on Botan, which is not available at this time within Craft.
As this change was not notified to Sysadmin and because it has left us in a state whereby we are unable to get the Windows CI system back up and running, this is being reverted so it can be brought back online.

Please reintroduce this change once support for having Botan as optional is restored

This reverts commit 47163784d74232e3a844fc42897bffc7eff817b4.