10.4.1 Although there is no option to make work types inactive you can still 'limit' the number of work types from the dropdown list on the Timesheet screen.
10.4.2 Do not assign 'All Work Types' on the Employee Billing Rates
Using 'All Work Types' on the Employee Billing Rates will list all work types even those that the employee is not authorized to perform
10.4.3 Give employees only the work types that they are allowed/expected to perform. This is the preferred option as it prevents employees from entering timesheets for work types they don't perform.
10.4.4 Update Work Types
If a work type has been changed make sure to update the employee billing rates
if a work type is no longer applicable then remove it from the employee billing rates