backend-wayland: drop unused pm_image
As @pq pointed out in !1130 (comment 1740847), this pixman image is not actually used anymore. Drop it.
Fixes: 89e1831c ("pixman-renderer: add weston_renderbuffer and create/destroy interface")
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As @pq pointed out in !1130 (comment 1740847), this pixman image is not actually used anymore. Drop it.
Fixes: 89e1831c ("pixman-renderer: add weston_renderbuffer and create/destroy interface")