switch to core question type labels instead of defining our own strings

src/pretix/base/datasync/sourcefields.py

@@ -529,19 +529,3 @@ def get_enum_opts(q):
         return [(opt.identifier, opt.answer) for opt in q.options.all()]
     else:
         return None
-
-
-QUESTION_TYPE_IDENTIFIERS = {
-    Question.TYPE_NUMBER: "NUMBER",
-    Question.TYPE_STRING: "STRING",
-    Question.TYPE_TEXT: "TEXT",
-    Question.TYPE_BOOLEAN: "BOOLEAN",
-    Question.TYPE_CHOICE: "CHOICE",
-    Question.TYPE_CHOICE_MULTIPLE: "CHOICE_MULTIPLE",
-    Question.TYPE_FILE: "FILE",
-    Question.TYPE_DATE: "DATE",
-    Question.TYPE_TIME: "TIME",
-    Question.TYPE_DATETIME: "DATETIME",
-    Question.TYPE_COUNTRYCODE: "COUNTRYCODE",
-    Question.TYPE_PHONENUMBER: "PHONENUMBER",
-}