MWTransclusionDialog: Remove setMode() call from teardown()

teardown() runs after the dialog has been hidden (if you need it
to be visible, use close() instead).

However removing it instead of moving because it is obsolete,
this is something that should be done from setup() instead, and
already is.

Bug: 65373
Change-Id: Ib6b4ab49f191d1d339e69934453786a82d97380f