sw: fix invalid downcast of SwDrawFrameFormat in DelContentIndex()

failure in UITest_writer_tests6:

sw/source/core/undo/undobj.cxx:1021:47: runtime error: downcast of address 0x61300019d3c0 which does not point to an object of type 'SwFlyFrameFormat'
    0x61300019d3c0:m note: object is of type 'SwDrawFrameFormat'
     a2 01 80 19  50 ac d1 9e 14 7f 00 00  00 af 19 00 30 61 00 00  e8 4f 0b 00 b0 61 00 00  40 dd 40 00
                  ^~~~~~~~~~~~~~~~~~~~~~~
                  vptr for 'SwDrawFrameFormat'
 in SwUndoSaveContent::DelContentIndex(SwPosition const&, SwPosition const&, DelContentType) at sw/source/core/undo/undobj.cxx:1021:47 (instdir/program/../program/libswlo.so +0xf8e5833)

Also lose the ridiculous overloading across derived classes.

Change-Id: I19439d0d511c5f8c36b00d8dd02c31f802a44e00
Reviewed-on: https://gerrit.libreoffice.org/83175
Tested-by: Jenkins
Reviewed-by: Michael Stahl <michael.stahl@cib.de>

0 files changed, 0 insertions, 0 deletions