60db3d2c "dbu: Set Firebird to default in
wizard.." had done so only "..in case experimental feature is checked in", but
Firebird has been made non-experimental meanwhile as documented at <https://
wiki.documentfoundation.org/index.php?title=ReleaseNotes/6.2&oldid=169290#Base>.

<https://bugs.documentfoundation.org/show_bug.cgi?id=123099> "Creating new
'HSQLDB Embedded' database immediately brings up migration-to-Firebird dialog"
discusses that changing the default to Firebird may be beneficial, so lets do
that unconditionally now.

But 60db3d2c had apparently made a mistake,
setting the value returned from OGeneralPageWizard::getDatasourceName to
"sdbc:embedded:firebird" even though the corresponding "Connect to an exisiting
database" list in the new database wizard doesn't even support that (instead of
"sdbc:firebird:", which matches "Firebird File" in that list).  Fixed that now.

(Curiously, ODsnTypeCollection::getEmbeddedDatabase would read a
DefaultEmbeddedDatabase value from the configuration before resorting to the
hardcoded default, but `git log -SDefaultEmbeddedDatabase` makes it look like
there has never been any code to actually write that setting.)

Change-Id: I49b7430f5f8288a6a166ed9184cb438208d56ca1
Reviewed-on: https://gerrit.libreoffice.org/67449
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>