common/canvas_base.c: remove unused variables
common/canvas_base.c: remove unused variables

fgouget/spice-common,freedesktop-unofficial-mirror/spice__spice-common,freedesktop-unofficial-mirror/spice__spice-common,elmarco/spice-common,fgouget/spice-common,elmarco/spice-common,fgouget/spice-common,Fantu/spice-common,freedesktop-unofficial-mirror/spice__spice-common,elmarco/spice-common,freedesktop-unofficial-mirror/spice__spice-common,Fantu/spice-common,fgouget/spice-common,Fantu/spice-common,SPICE/spice-common,SPICE/spice-common,SPICE/spice-common,Fantu/spice-common,elmarco/spice-common