fdo#67104 Use correct command for show grid

Not sure why .uno:ViewGridLines & SID_SCGRIDSHOW were
introduced (in "merge sidebar feature" and related commits).

Change-Id: I90bdfaef86adcbfa44129b8f7f9df61ca7f35114
Reviewed-on: https://gerrit.libreoffice.org/8459
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>