TheiaCon 2023 Website - Update member logos

The members list on https://events.eclipse.org/2023/theiacon/ needs some minor updating, as follows:

1. We now have a single membership level. So, we need to remove remove the "Strategic Members" and "Participating Members" headers
2. IBM and SAP are no longer members and need to be removed.
3. Show the remaining 9 logos in alphabetical order, similar to https://ecdtools.eclipse.org/membership/

Thank you!

@serina FYI