No. This is a medical myth that makes things easier for an attending physician but has no actual effect on your birth experience. Unless you want one, you can refuse.
No. This is purely a choice. Some women are afraid of having a bowel movement during labor and pushing so they prefer an enema, but it is not necessary.
There is no need to have an enema prior to childbirth. If you are constipated, you can be sure that the process of labor and pushing a full-term baby out of you will move everything in your intestines out as well.
No. Many years ago this used to be standard practice, but this is no longer the case. Your body naturally tends to soften or clean out your bowels prior to giving birth.