gnu: Remove unneeded libxml2 from native-inputs. (libxslt)

XML_CATALOG_FILES is already set within libxslt so it's unnecessary to include
libxml2 for the same effect.

* gnu/packages/freedesktop.scm (wayland): Remove obsolete comment.
(farstream, elogind, packagekit, accountsservice, plymouth)[native-inputs]:
Remove libxml2.
* gnu/packages/benchmark.scm (sysbench)[native-inputs]: Ditto.
* gnu/packages/cluster.scm (drbd-utils)[native-inputs]: Ditto.
* gnu/packages/glib.scm (dbus)[native-inputs]: Ditto.
* gnu/packages/gnome.scm (gnome-keyring, glade3, dconf, libsecret, colord)
(upower, gnome-settings-daemon)[native-inputs]: Ditto.
* gnu/packages/linux.scm (eudev)[native-inputs]: Ditto.
* gnu/packages/networking.scm (iputils)[native-inputs]: Ditto.
* gnu/packages/ocr.scm (tesseract-ocr)[native-inputs]: Ditto.
* gnu/packages/polkit.scm (polkit)[native-inputs]: Ditto.
* gnu/packages/samba.scm (samba/pinned)[native-inputs]: Ditto.
* gnu/packages/sssd.scm (adcli)[native-inputs]: Ditto.
* gnu/packages/terminals.scm (kmscon)[native-inputs]: Ditto.

Signed-off-by: Maxim Cournoyer <maxim.cournoyer@gmail.com>
Change-Id: Ica3fb5a8e23ad928c53ae508c02777d78c635af0

gnu/packages/glib.scm

@@ -161,7 +161,6 @@
            docbook-xsl
            doxygen
            libtool
-           libxml2 ;for XML_CATALOG_FILES
            libxslt
            which
            xmlto