[lua] Fix Water Way to Go trade item not consumed on completion

[Millhouse1337]

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What does this pull request do?

Closes #7926.

When the player trades the Canteen of Giddeus Water to Ohbiru-Dohbiru to complete Water Way to Go, the gil reward is granted but the canteen is not removed from inventory. The bug is in the handler for event 355 (the quest-completion cutscene): it called player:tradeComplete() instead of player:confirmTrade(), so the trade items were never consumed.

This PR replaces that single call. confirmTrade() matches the canonical pattern used by every other Windurst trade-completion quest:

• scripts/quests/windurst/A_Smudge_on_Ones_Record.lua (event [417])
• scripts/quests/windurst/Blast_from_the_Past.lua (event [224])
• scripts/quests/windurst/All_At_Sea.lua (event [295])
• scripts/quests/windurst/Curses_Foiled_Again_1.lua (event [173])

…and the working event [55] handler in this same file (the earlier trade where the Giddeus Spring fills the empty canteen).

Steps to test these changes

On a character that has completed Overnight Delivery and has Windurst fame ≥ 3:

1. !addquest 2 16 (adds Water Way to Go in QUEST_ACCEPTED state)
2. !additem 4351 (Canteen of Giddeus Water)
3. Travel to Windurst Waters and trade the canteen to Ohbiru-Dohbiru
4. Watch the cutscene complete

Verify after the event:

• Water Way to Go shows as completed in the quest log
• Player gained 900 gil
• Canteen of Giddeus Water is no longer in inventory (this was the bug)