I need to delete all system.debug statements in all the apex classes. Is there any method we can mass comment/delete the debug statements in one go?
There is not an "automated" way to do this. Using Eclipse, you might be able to use a Find/Replace with a Regex to possibly do this, but you would want to be very careful not to corrupt the code base. The only non-Eclipse way I can think of, would be to do an export of the codebase using something like the ANT migration tool, then use a text editor that can scan and update multiple files at the same time. Of course, once you update all of the code, you would need to save it back into Salesforce again.