Use wpilib's builtin StructGenerator instead of custom RecordStruct

[Daniel1464]

WPILib now has a struct generator class that already generates structs for record classes, so there's no need for akit to still have its own.

[jwbonner]

Does the WPILib StructGenerator support enum fields nested within a record? These lines seem to suggest not, though perhaps I've missed something. Otherwise this looks OK to me, but maintaining that support would be a prerequisite to switching.