They'll probably continue to do door-to-door proselytizing in some areas and under certain circumstances.
This article more or less explains the new policy. Knocking on doors has long been recognized as perhaps the least effective way there is to find potential converts, and the Church is becoming well-enough known that in many parts of the world, the missionaries don't have to look that far for people who are interested in learning about it. Most converts these days are the result of referrals from members of the Church whose friends have expressed an interest in learning more.