fdo#38844 Remove XOR rendering code from canvas module

Change-Id: Ie0c6b2950184bd3843baae59eff08a2f4e9e1b9c
Reviewed-on: https://gerrit.libreoffice.org/8715
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>