use DATAVERSE_SITEURL instead of _CT_ version

[pdurbin]

The _CT_ version is not needed now that we have upgraded to Payara 6.2024.6 in #10495 which included this fix: payara/Payara#6550

What this PR does / why we need it:

Which issue(s) this PR closes:

• Closes Change _CT_DATAVERSE_SITEURL to DATAVERSE_SITEURL #10756

Special notes for your reviewer:

Please see the detailed commit message.

Suggestions on how to test this:

• Follow the quickstart at https://guides.dataverse.org/en/6.3/container/running/demo.html using the compose file in this PR, of course.
• Create a dataset and publish it
• Click "Metadata" then "Export Metadata" and note that the value in DATAVERSE_SITEURL (https://demo.example.org) is used. You can change this value before running docker compose up if you like.

Does this PR introduce a user interface change? If mockups are available, please link/include them here:

No.

Is there a release notes update needed for this change?:

No, not worth it.

Additional documentation:

None.