Skip CPS validation checks if using `selectChains` filter

The CPS group validity checks require that every group has at least two members, as running CPS on a single HLT chain accomplishes nothing. This frequently triggers if the selectChains option is used in runHLT_standalone to run only a small number of triggers, which is inconvenient, and then requires a user to set the Trigger.disableCPS config flag in addition.

This change checks the menu's chainFilter to see if this option has been used, and in this case disables the validity checks, to make testing specific chains less frustrating. As this should also avoid crashes in the TrigID ART tests, the disableCPS check does not need to stay enabled for those. The flag is retained in case it is needed for any other reasons.