Translate some German comments to English in sw/source/core/text/txtfrm.cxx.

Change-Id: I54ee2e7341edbe3bbfe6429bedb4315a64bfb593
Reviewed-on: https://gerrit.libreoffice.org/7481
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>