Revert "[mms] Use more efficient date sorting algorithm as the default choice."

This reverts commit 4c184a38944a62e3cbd892fe384eb3b80e0b3a42.

Conflicts:
	imp/docs/CHANGES
	imp/package.xml

On further reflection: this is not a valid change.  Sequence sort is the
order in which messages were processed by the IMAP server.  It is not
directly related to when a message was received on the server.
Default sort should be sequence sort, since it is the least expensive sorting algorithm
More accurate description of sequence sort
Bug #12139: Correct usage of arrival vs. sequence for sorting