What is the antonym of "to get used to"?
Solution 1:
"Wean" seems to be the closest word to what you're looking for:
wean somebody off/from something (phrasal verb): to make someone gradually stop doing something you disapprove of:
advice on how to wean yourself off nicotine
to detach from a source of dependence:
being weaned off the medication
wean the bears from human food
also : to free from a usually unwholesome habit or interest:
wean him off his excessive drinking
weaning them from habits of violence — Geoffrey Carnall
However, "getting out of the habit of ..." is a very clear and understandable phrase.
Update:
A few other alternatives from subscription-only LDOCE (See the last item which is quite an antonym, but still different in the meaning):
leave off (phrasal verb): to stop doing something:
'Will you leave off nagging?' he snarled.
break/kick a habit (=stop doing something that is bad for you):
I've smoked for years, but I really want to kick the habit.
unaccustomed (formal) unaccustomed to (doing) something: not used to something:
a country boy, unaccustomed to city ways
Register: In everyday English, people usually say that they are not used to something rather than unaccustomed to it.
Solution 2:
try dishabituate:
To render unaccustomed to or unfamiliar with.