This reverts commit 950a5300dc.
Reason for revert: This broke several workflows. The reason is
that MWParameterPlaceholderPage & MWParameterSearchWidget both
hold references to the MWTemplateModel. This model is not
always the same. The dialog might be the same when a template
is edited multiple times. But the model might be a new one.
From this point on the MWParameterSearchWidget pulls data from
an outdated model.
Bug: T284636
Bug: T285571
Change-Id: I7b9ea8cab8f17705ec8020f07e3732da6ba0e73c
e6d3828429