Remove ME0 from HGCal custom (but not HGCalMuon)

HGCalMuon and HGCalMuon4Eta have ME0 but HGCal does not.  Previously they both used the same customisation and so HGCal (142xx) failed in step 2 because it couldn't find the ME0 hits.  With this pull request the customisations are diverged.

The effective only change is that HGCal calls cust_2023Pixel() before applying the HGCal specifics.  It previously called cust_2023Muon() instead.  HGCalMuon and HGCalMuon4Eta still call cust_2023Muon().

The consequence is that HGCal no longer has these two lines in the customisation sequence:

    process=customise_rpc(process)
    process=customise_me0(process)

**@ianna, is it correct to remove the customise_rpc call as well?**  I did it this way because it was easier to delegate to the cust_2023Pixel function.

After this change the 142xx tests run through step 2 and fail in step 3 with the same crash as all the others.