Add POH heads drops

What has been done in this MR?

• Fix #1619 (closed)
• Removed basilisk head from main drops
• Added all heads (including basilisk) as tertiary drops (thanks for the tip, Ryan!). Sources: Basilisk head 1:2000 https://runescape.wiki/w/Basilisk Cockatrice head 1:1000 https://runescape.wiki/w/Cockatrice Abyssal head 1:5000 https://runescape.wiki/w/Abyssal_head Crawling hand 1:512 https://runescape.wiki/w/Crawling_hand\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\_(item) Kurask head 1:3000 https://runescape.wiki/w/Kurask_head KBD & KQ: #1619 (closed)
• (Sources are all current-RS3 rather than 2009, because this is the only place not called OSRS where I could find actual rates)

What should testers check?

• Heads drop as expected. I recommend rolling no fewer than 1M drops to ensure you get stable results.

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

Screenshots: