The Fremennik Exiles: Minor polish

[pajlada]

• Removed the duplicate sidebar step as noted in this discord message
• Added the missing sidebar step as noticed by the sidebar step test (and also noted by the above discord message)
• Prioritized the "Pick up letter" part of the first quest section, ensuring the user isn't told to search the sandpit if the letter is on the ground.
• Add a missing dialog step that you might need to click if you cancel out of a conversation at the start of the investigation with Brundt
• Re-implemented the "talk about the shield with Brundt" substeps. I tested all of these during the quest & everything worked as expected, with the fallback step just being "talk to him about everything".

Fixes #1928