pkg-config doesn't use message translation, so there's no need to build
it into the bundled glib. Furthermore, when not using glibc, this drags
in extra dependencies on gettext, libintl and iconv. Remove their usage
in two steps:
1. Don't include libintl.h directly from code. glibintl.h
conditionalizes the include of libintl.h based on the ENABLE_NLS define
and creates fallback macros when it's unwanted.
2. Remove the usage of the gettext macros in glib's configure.ac. This
ensures that the unwanted dependencies aren't searched for. Two defines
are kept around to keep the code happy.
