Remove orphaned attributes

[peterjaap]

• Create a list of all product attributes from the database
• Search through the codebase to see whether they are mentioned in InstallData/UpdateData scripts - those are fine
• Search through phtml files to see whether they are used (also make sure to look for getAttributeName / setAttributeName instead of just attribute_name) - those are fine
• We should whitelist all core attributes since those have names that occur a lot ('name' / 'sku')
• The remaining product attributes might be removeable

This probably can't be done automatically since it'll most likely show too many false positives.