mv_machine_learning: use MachineLearningConfig class for other task groups

mv_machine_learning: use MachineLearningConfig class for other task groups

[Issue type] : code refactoring

Use MachineLearningConfig class for other task groups instead of internal ones.

We have introduced a new common config class[1] and object detection and
object detection 3d task groups use already it. So this patch makes
other task groups - which not use the common config class - to use the
common class instead of internal ones, and drop the internal config class.

In addition, this patch applies confidence threshold config key for
landmark detection task group to MachineLearningConfig class.

[1] https://review.tizen.org/gerrit/#/c/platform/core/api/mediavision/+/301043/

Change-Id: I6e77ce33349bbdcb22f64102a7ec3f8808249b1c
Signed-off-by: Inki Dae <inki.dae@samsung.com>