Remove / Hide the "Approval" and "Collect Feedback" workflow in the "Start a New Workflow" page.

Solution : Go to : Shared Service Administrator > Site Setting > Site Content Type Gallery > Site Content Type,

Select 'Document' or that content type where you want to remove 'Approval' or 'Collect Feedback' OOB Workflows.

Click 'WorkFlow Settings' > remove the 'Approval' and 'Collect Feedback'

It is recommended to create your own site content type to do this otherwise all those document libraries will be affected which have that content type.