Remove call to setPadding() in setUseDefaultMargins().

It is not possible for teh user to override the assigned padding values
because the XML attributes are processed in the opposite order.

Also, make the XML and Java examples grid3.xml and Activity2.java
consistent in preparation for a move to API demos.

Change-Id: I47334f9f5a46a8a528067d88350dd70eaa38ff33