Related bnc#822625: Minimum height was not invalidated when rectangle changes.

5792e76cb5beb630c135f57b74f57d74dd2dc2b0 was too optimistic and did not
invalidate mnCachedMinHeight often enough.
This was resulting in a grey area below table frame when resizing it.

So, revert 5792e76cb5beb630c135f57b74f57d74dd2dc2b0
"Related bnc#822625: Cache minimum height for table cells."
and istead just use getMinimumWidth() in TableLayouter if that's all we need.
getMinimumHeight() is expensive.

Change-Id: I34c49dda75d6ccccaa5b4d3746114352621a40dd
(cherry picked from commit b8f7ea5da41d61d405adec54dcd10b54ee0e5591)
Reviewed-on: https://gerrit.libreoffice.org/9870
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>