[AI-FSSDK] [FSSDK-12337] Remove redundant tests, keep 6 essential ones

Removed 7 tests that were covered by other tests:
- test_experiment_type_field_parsed (covered by injection test)
- test_feature_rollout_with_empty_rollout_experiments (similar to no_rollout)
- test_feature_rollout_multiple_experiments_mixed_types (covered by injection + unchanged)
- test_feature_rollout_flag_variations_map_includes_injected (subset of maps test)
- test_experiment_type_ab (just string assignment)
- test_feature_rollout_with_variables_on_everyone_else (edge case)
- test_existing_datafile_not_broken (covered by none_when_missing + unchanged)

Author: FarhanAnjum-opti