fix: delete flaky TestGetCourseUserPartitions tests

[robrap]

The following TestGetCourseUserPartitions tests were deleted:

• test_enrollment_track_partition_not_added_if_conflict
• test_enrollment_track_partition_not_added_if_disabled

For details, see: https://github.com/openedx/edx-platform/issues/35028

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[edx-pipeline-bot]

2U Release Notice: This PR has been deployed to the edX staging environment in preparation for a release to production.

[edx-pipeline-bot]

2U Release Notice: This PR has been deployed to the edX production environment.