Remove equipableSchema from itemUpgrade

Intent

EquipableSchema was added to itemUpgradeSchema during the initial work, this was a mistake.

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• This is meant for a hotfix
• This is meant for the next release (see milestone)
• This needs more reviewers than normal; there may be controversy or high complexity
• This intentionally introduces regressions that will be addressed later
• There is/will be documentation changes on the wiki
• Please do not send commits here without coordinating closely with the owner
• This is a Build System change

Related Issues

• #938 (closed)

Steps to Test

1. Read the diff