Remove TrainingStagePar.json

[alexpiet]

Pull Request instructions:

• Please follow the update protocol
• Answer the questions below in detail. Your responses will be emailed to experimenters.
• If the experimenters must do anything new, provide detailed step by step instructions on the wiki
• If computer maintainers need to manually update anything, provide detailed step by step instructions
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Describe changes:

• TrainingStagePar.json is an outdated json file that contained definitions of the training stages before we used AutoTrain. I'm removing the file, the UI widgets, and the code that loaded and used those features
• Also adds AttenuationRight to list of mandatory fields in Settings_box#.csv

What issues or discussions does this update address?

• resolves #497

Describe the expected change in behavior from the perspective of the experimenter

New UI

Old UI

Describe any manual update steps for task computers

• None

Was this update tested in 446/447?

• [x] tested in 447

[alexpiet]

@hanhou @XX-Yin This is ready for review