You can't. Yet another Microsoft failure.
See e.g. "If you have Office 365 you cannot uninstall individual applications" (http://answers.microsoft.com/en-us/office/forum/office_2013_release-onenote/how-do-i-uninstall-onenote-from-office-2013/2fb1f12d-7cc5-4004-8b39-d0f4d22d84da)
Someone on that page did mention that it (which he calls "App Exclusion" during installation) is coming.
-----------------------------------------------------------------------------------------*
Probably not a great idea, but you could of course delete various files, such as:
• C:\Program Files\Microsoft Office 15\root\office15\ONENOTE.EXE
• C:\Program Files\Microsoft Office 15\root\office15\ONENOTEM.EXE (that annoying "Send to OneNote" item in the tray)
A temporary workaround, I know, but at least this way they won't pop up and annoy you.