buildroot

ding-libs: use the new gettext logic

This commit switches to use the new gettext logic, which involves:

 - using TARGET_NLS_DEPENDENCIES instead of hand-encoded dependencies
   on gettext/host-gettext

 - dropping BR2_PACKAGE_GETTEXT selection

The BR2_USE_WCHAR dependency was only needed for gettext. But now, we
no longer need gettext unconditionally, so this dependency on
BR2_USE_WCHAR is removed.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>