gawk: trim native build configuration

gawk: trim native build configuration

When we build gawk-native it is only for use in builds where the host
gawk output isn't reproducible across versions[1]. As such it doesn't
need support for readline or mprf, and by removing those from gawk-native
we can get building gawk-native sooner.

[1] oe-core c5bbf0a60b ("gawk: use native gawk when building glibc and grub")

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>