Fixed exception on server boot related to a duplicated attempt to register dialogue for Jarvald

Depends on 2009scape/tools/rs09-constants-library!18 (merged), will fail to compile without it.

What has been done in this MR?

• Removed leftover code from before Jarvald was ported to Kotlin. Fixes #1963.
• Corrected a Jarvald NPC ID in constlib and made the server code use that instead of the raw number.

What should testers check?

• Check that Jarvald's dialogue still opens normally. NPC IDs 2435-2438.

• I have tested these changes thoroughly.

• I used the relevant Zaros tool for any JSON edits where possible, and have attached screenshots of any changes.