YmLWh‖Delete All Comments

aEbAx‖Deletes all cell notes of the current sheet.

To access this command...

ebLJB‖From the menu bar:

e6Jua‖Choose Sheet - Cell Comments - Delete All Comments

qBbLh‖From the tabbed interface:

9q47y‖Choose Review - Delete All Comments.

sXy2C‖From toolbars:

nxKGZ‖Icon Delete All Comments

3bVhn‖Delete All Comments