Remove the 'BUILTBYEXPERIMENTALSUB' category from various units

[Basilisk3]

Description of the proposed changes

Removes the BUILTBYEXPERIMENTALSUB category from various units.

Testing done on the proposed changes

The Tempest can still build these units just fine. Except units like the Seraphim cruiser of course, interestingly enough, this unit also had the category.

Additional context

According to @The-Balthazar on Discord, this category is unused.

Checklist

• Changes are documented in the changelog for the next game version

[The-Balthazar]

If the Tempest ever used BUILTBYEXPERIMENTALSUB, it was in the original beta. In SupCom1 it's got the same build categories as it does in FA. BUILTBYEXPERIMENTALSUB exists in a lot of mods, but because they uncritically copied the blueprints of the units this PR removes it from, not because they planned to use it; same reason non-Aeon FA units appear to have it, at least as far as my searches have gone.