installer: Remove "selection" from all titles.

installer: Remove "selection" from all titles.

* gnu/installer/newt/hostname.scm (run-hostname-page): Remove selection from
page title,
(run-variant-page): ditto.
* gnu/installer/newt/keymap.scm (run-layout-page): Ditto.
* gnu/installer/newt/locale.scm (run-layout-page): Ditto,
(run-territory-page): ditto,
(run-codeset-page): ditto,
(run-modifier-page): ditto
* gnu/installer/newt/network.scm (run-territory-page): Ditto.
* gnu/installer/newt/timezone.scm (run-timezone-page): Ditto.
* gnu/installer/newt/wifi.scm (run-wifi-page): Ditto.