prevent duplicated conditional formatting during copying of sheeets

Change-Id: I866c0c4c05830af0070767aec36375a846a2bf84
Reviewed-on: https://gerrit.libreoffice.org/11326
Reviewed-by: Kohei Yoshida <libreoffice@kohei.us>
Tested-by: Kohei Yoshida <libreoffice@kohei.us>