How to remove the computer name, date, and time at the bottom of every printed page
Rather than guess what has changed, here is a procedure to narrow the cause down.


Make a new user account from System Preferences and log into that user.
Open TextEdit and type one word or two and then print.


Don't change any settings and just print one page. If the page prints with the banner, then you can conclude that a system wide print setting has changed or that the printer itself is injecting the footer. The first thing I would try in this case is to reset the printing system:


http://support.apple.com/kb/HT1341
If you have printers - option click the - to reset pringing
if you have no printers, control click the area above the +/- control and reset the printing system


It would be odd to still have banners after resetting the print system and possibly something the print driver is doing automagically.

If not, you can know that it's a print default setting that was entered for your user account.