gnu: Remove meson-0.59 workarounds.
Mostly automated with the following command:
$ grep --include='*.scm' '#:meson ,meson-0.59' -rl \
| xargs sed -z 's/#:meson[^\n]*\s*//' -i
* gnu/packages/freedesktop.scm (malcontent)
(accountsservice): Delete #:meson argument.
* gnu/packages/games.scm (gnome-2048): Likewise.
* gnu/packages/geo.scm (gnome-maps): Likewise.
* gnu/packages/gnome.scm (gnome-photos, gnome-music)
(gnome-initial-setup, gnome-user-share, gnome-characters)
(gnome-disk-utility, gnome-font-viewer, evince, glade3)
(gnome-mines, gnome-sudoku, gnome-settings-daemon, devhelp)
(totem, eog, gvfs, simple-scan, epiphany, gnome-session, gedit)
(network-manager-applet, gnome-control-center, gnome-shell, nautilus)
(gnome-default-applications, gnome-weather, gnome-tweaks, cheese, gthumb)
(gitg, polari, gnome-boxes, gtranslator): Likewise.
* gnu/packages/gtk.scm: (gtkmm-3): Likewise.
* gnu/packages/pdf.scm (zathura): Likewise.
* gnu/packages/photo.scm (entangle): Likewise.
* gnu/packages/video.scm (pitivi): Likewise.
* gnu/packages/virtualization.scm (libvirt-glib): Likewise.