Removed dependency on IDP-Installer.conf file

IDP-Installer.conf file no longer needed for configuring idp version and
has been removed. This should ensure consistency.
Deleted unused file IDP-Installer.conf

Configuration file was superseded by group_vars and was no longer
needed.
Merge pull request #51 from ausaccessfed/feature/remove-idp-conf-file

Removed the need for an IDP-Installer.conf file
Resolves #49