see 706ac477 and fdo#47589

The original code lead to invoking a pure virtual function in Calc when
doing Ctrl-F2, ESC.

This reverts commit 9a11bd42.
Removing attributes from the _source_ node in SwTxtNode::MakeCopy does
not make any sens at all, and the cited issue i#96092 was apparently
fixed independently in CWS sw31bf04 by the change to ndtxt.cxx in
1524aa18.

Using XMultiPropertySet reduces the number of SwTxtNodes created for the
bugdoc from rhbz#789022 from ~5k to ~3k.

SwNodes::UpdateOutlineNode will add/remove the node from
SwNodes::pOutlineNds depending on IsOutline(), while various SwNodes
methods that move and delete nodes check GetAttrOutlineLevel() != 0,
which may be false even if IsOutline() is true.