remove vhd setup

[rerpha]

Removes lots of VHD specific setup steps as:

1. the vhd build has been disabled for ages on jenkins
2. we are moving towards using ansible to deploy software instead of using VHDs.

[Tom-Willemsen]

minor nit, otherwise looks good.

Could also delete most or all of https://isiscomputinggroup.github.io/ibex_developers_manual/deployment/future_workflows/Mount-or-create-IBEX-VHDs.html

[rerpha]

Could also delete most or all of https://isiscomputinggroup.github.io/ibex_developers_manual/deployment/future_workflows/Mount-or-create-IBEX-VHDs.html

ISISComputingGroup/ibex_developers_manual#216