Revert "PJSIP_CONTACT: add missing argument documentation"

This reverts commit 7e3015d7.

Reason for revert: Regression in XML validation.

validity error : Content model of enumlist is not determinist:
(configOptionToEnum | (configOptionToEnum , enum+) | enum+)

As we are preparing to do releases and this is not critical
I am reverting this for now until resolved.

Change-Id: I30c2295f9d7f0a0475674ee77071a7ebabf5b83f