Open the event that contains the sticker. It will move the sticker to the upper right corner. Tap on the sticker and an option menu will slide up with the sticker. Tap the red minus sign next to it and it should remove it.
Hi, CLF. Your instructions remove the sticker from one particular event. I believe the original poster was asking how to disable stickers completely, as the happy-face icon takes up too much space when looking at the overall calendar, taking up space equal to a whole hour's worth of the screen.
In month view I only see one small grey sticker hint and it's displayed on the current day of the week. It's only shown if the current day has no entries.
Use stickers, don't use stickers the choice is yours. I don't know of any way to remove the stickers option.