Remove unsupported databases from installation wizard

During the Confluence installation Wizard, options for the database are listed which are unsupported. This can be misleading and and cause confusion to user (aka, why would we offer them if we do not support them). As of 5.2.3, the following are listed and I would advise removing them.

• DB2
• Sybase ASE
• Oracle 8i
• Oracle 9i/10g

What we can keep is the 'unsupported' option which leaves no room for confusion.