Correctly insert at an existing parent if appropriate

At the end of a string (Case 2) the undo of a deletion of a placeable
(e.g. an XML tag) would be restored as plain text instead of part of
the existing tag.
Revert "Correctly insert at an existing parent if appropriate"

This reverts commit bb04ce073bfd5e1543285074b20fedf54d3f6feb.

Tests are failing because of this change. Nothing seems wrong with the
change but it needs a fix to the related tests before it lands again.