Remove unused locales

This reduces the size of the (compressed) image by a few megabytes.

build-rootfs.sh

@@ -38,6 +38,9 @@ ${target}-emerge -vnj \
     sys-kernel/linux-firmware \
     --
 
+ROOT=/mnt/gentoo \
+locale-gen
+
 mkdir -p \
     /mnt/gentoo/boot/efi \
     /mnt/gentoo/dev \

overlay/etc/locale.conf

@@ -0,0 +1 @@
+LANG=en_US.UTF-8

overlay/etc/locale.gen

@@ -0,0 +1 @@
+en_US.UTF-8 UTF-8

portage/make.conf/40-lang.conf

@@ -0,0 +1,3 @@
+LINGUAS=en
+L10N=en-US
+USE="${USE} -nls"