It removes the HACK where the doc model was changed.
We introduce a pointer to a surrounding frame: an indicator
telling us that the table was placed in a frame to make it
floating.

During export, remove the frame and use the relative width of the
surrounding frame.

Change-Id: I43b45d9a9e67ee755782c9f18df22ae1d4014689
Reviewed-on: https://gerrit.libreoffice.org/67775
Tested-by: Jenkins
Reviewed-by: Miklos Vajna <vmiklos@collabora.com>