[lua] Various battlefield superlinking setup

[Skold177]

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What does this pull request do?

Fixes superlinking in several battlefields by letting it be handled by the battlefield framework. A follow up to Franks PR.

• Battlefields where the monsters are grouped in a single bracket (all spawned at once) are now defined with superlink = true

• Battlefields where the monsters are in different brackets due to being spawned at different points during the fight are now linked with superlinkGroup = 1,

• Battlefields setup with content:addEssentialMobs already have superlink applied automatically.

• Removes superlink mobmod from several enemies, as it is no longer needed.

Steps to test these changes

Run Automaton Assault, Wyrmking Descends, When Hell Freezes Over, Steamed Spouts or any of the other changed BCNMs, see superlink now works.