Also removes dead code because SwTabFramePainter::Insert()
is always called with a cell frame and IsTabFrame() always
returns false.

Reviewed-on: https://gerrit.libreoffice.org/54684Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
(cherry picked from commit e87cc12e)

Conflicts:
	sw/qa/extras/layout/layout.cxx
	sw/source/core/layout/paintfrm.cxx

(cherry picked from commit 948283ca)

Change-Id: I2505d876d20e44ded1faf760bc3b7b1d34b0fd8d