xwayland: Drop the separate refcount for the xwl_pixmap

Instead, bump the pixmap's refcount at the bottom of post_damage to
reflect the compositor's hold on the buffer, and "destroy" the pixmap in
the buffer release callback (which will dec the pixmap's refcount and
free if necessary).

Signed-off-by: Adam Jackson <ajax@redhat.com>
4 jobs for xwayland-no-xwlpixmap-refcount in 7 minutes and 10 seconds (queued for 3 seconds)
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debian-testing

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autotools

00:06:32

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meson

00:01:56

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meson-noglamor

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