Cairo 1.17.2 requires at least Pixman 0.36.0, so update to the latest
and greatest version [0.38.0][1].

> Changes since 0.36.0:
> - Use floating point calculations for gradients and pixman-bits-image when
>   better accuracy is requested.
> - Add support for the meson build system.

[1]: https://lists.freedesktop.org/archives/pixman/2019-February/004838.html

[Announcement][1]:

> This snapshot provides the new support for writing floating point
> formats as 16 bpc PNGs, with support for RGBA128F and RGB96F formats.
> This new feature increases Cairo's pixman version requirement to 0.36.0.
>
> Beyond this are a range of bugfixes and some work on establishing CI for
> Cairo.

[This fixes the printing problem with a PDF document from the
FU.](https://github.com/OpenPrinting/cups-filters/issues/93)

The Cairo issue is [Cairo generates incorrect PDF files]
(https://gitlab.freedesktop.org/cairo/cairo/issues/342).

Remove patch, applied upstream.

[1]: https://lists.cairographics.org/archives/cairo-announce/2019-February/000224.html