Fix flaky TestGetCourseUserPartitions tests

Following the old Flaky Test Process, I've deleted two flaky tests.

The deletion PR is https://github.com/openedx/edx-platform/pull/35029.

The following tests were deleted:

• TestGetCourseUserPartitions.test_enrollment_track_partition_not_added_if_conflict
  • Link to failure https://github.com/openedx/edx-platform/actions/runs/9616581879/job/26526428843 that passed after re-running.
• TestGetCourseUserPartitions.test_enrollment_track_partition_not_added_if_disabled
  • Link to failure https://github.com/openedx/edx-platform/actions/runs/9641692755/job/26587890635 that passed after re-running.

Notes/Questions:

• The only recent partition-related change seems to be: https://github.com/openedx/edx-platform/pull/33788
• Separately, we might want to ticket updating the Flaky Test Process, but where?
  • I wrote up https://discuss.openedx.org/t/flaky-test-process/13263
• The class has one last test, test_filter_inactive_user_partitions, which may also be flaky but I didn't see it yet so I left it in the code.

Failure 1:

=========================== short test summary info ============================
FAILED xmodule/partitions/tests/test_partitions.py::TestGetCourseUserPartitions::test_enrollment_track_partition_not_added_if_conflict - AssertionError: assert 1 == 2
 +  where 2 = len([UserPartition(id=0, name='Mock Partition', description='for testing purposes', groups=[Group(id=0, name='Group 1'), G...serPartitionScheme object at 0x7f3198774dd0>, parameters={'course_id': 'course-v1:org_0+course_0+run_0'}, active=True)])
==== 1 failed, 1487 passed, 170 skipped, 1572 warnings in 229.69s (0:03:49) ====

Failure 2:

=========================== short test summary info ============================
FAILED xmodule/partitions/tests/test_partitions.py::TestGetCourseUserPartitions::test_enrollment_track_partition_not_added_if_disabled - AssertionError: assert 1 == 2
 +  where 2 = len([UserPartition(id=0, name='Mock Partition', description='for testing purposes', groups=[Group(id=0, name='Group 1'), G...serPartitionScheme object at 0x7f6d54d9e9d0>, parameters={'course_id': 'course-v1:org_0+course_0+run_0'}, active=True)])
==== 1 failed, 1487 passed, 170 skipped, 1572 warnings in 229.98s (0:03:49) ====