Correct mw.PopUpMediaTransform dependency

mw.PopUpMediaTransform actually only has a direct depdendency on
mw.MwEmbedSupport, which provides mw.addDialog.  This makes a
difference since mw.MwEmbedSupport only loads jquery.ui.dialog
dynamically if an actual dialog is shown.

Bug: 55550
Change-Id: I578c93c3036b661f6e4fea9723212e0b9b7b216f
Merge "Correct mw.PopUpMediaTransform dependency"