Remove HPD specific RICH code

Big cleanup of the RICH codebase, removing code specific to HPDs.

This MR is a cleaning out a lot of now obsolete code, as a first step towards a future MR that will add support for a realistic PMT encoding and decoding.

There will be a number of updates in other LHCb projects to adapt.

Lbcom!486 (merged) Rec!2126 (merged) Boole!286 (merged) Panoptes!112 (merged) Moore!551 (merged) Brunel!1038 (merged)

@seaso @bmalecki FYI