fix: respect ENABLE_NEW_STRUCTURE_DISCUSSIONS flag in course import #21334

Job	Run time
python-3.8,django-pinned,lms-1	10m 32s
python-3.8,django-pinned,lms-2	8m 41s
python-3.8,django-pinned,lms-3	15m 26s
python-3.8,django-pinned,lms-4	17m 58s
python-3.8,django-pinned,lms-5	9m 16s
python-3.8,django-pinned,lms-6	15m 1s
python-3.8,django-pinned,openedx-1-with-lms	12m 35s
python-3.8,django-pinned,openedx-2-with-lms	14m 6s
python-3.8,django-pinned,openedx-1-with-cms	7m 11s
python-3.8,django-pinned,openedx-2-with-cms	4m 24s
python-3.8,django-pinned,cms-1	2m 44s
python-3.8,django-pinned,cms-2	14m 56s
python-3.8,django-pinned,common-with-lms	8m 43s
python-3.8,django-pinned,common-with-cms	4m 1s
python-3.8,django-pinned,xmodule-with-lms	4m 59s
python-3.8,django-pinned,xmodule-with-cms	4m 59s
python-3.8,django-4.2,lms-1	10m 18s
python-3.8,django-4.2,lms-2	9m 5s
python-3.8,django-4.2,lms-3	15m 14s
python-3.8,django-4.2,lms-4	18m 16s
python-3.8,django-4.2,lms-5	8m 26s
python-3.8,django-4.2,lms-6	15m 24s
python-3.8,django-4.2,openedx-1-with-lms	12m 41s
python-3.8,django-4.2,openedx-2-with-lms	14m 12s
python-3.8,django-4.2,openedx-1-with-cms	7m 5s
python-3.8,django-4.2,openedx-2-with-cms	4m 23s
python-3.8,django-4.2,cms-1	2m 45s
python-3.8,django-4.2,cms-2	14m 57s
python-3.8,django-4.2,common-with-lms	8m 47s
python-3.8,django-4.2,common-with-cms	3m 58s
python-3.8,django-4.2,xmodule-with-lms	5m 17s
python-3.8,django-4.2,xmodule-with-cms	4m 57s
compile-warnings-report	9s
Unit tests successful	2s
coverage (3.8)	1m 43s
	5h 13m 11s

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