[__locale_system] fix for debian and ubuntu

ubuntu 6.10 and debian etch are 10+ years old and EOL. rather than
preserving compatibility I'll just remove it. while /etc/environment
works too, correct place is /etc/default/locale (as it was before
breaking change). also /etc/debian_version (os_version explorer) may
contain minor version with dot (10.5) or string (bullseye/sid).

cdist/conf/type/__locale_system/manifest

@@ -40,27 +40,13 @@ os=$(cat "$__global/explorer/os")
 case $os
 in
     debian)
-        os_version=$(cat "${__global}/explorer/os_version")
-        if expr "${os_version}" '>=' 4 >/dev/null
-        then
-            # Debian 4 (etch) and later
         locale_conf="/etc/default/locale"
-        else
-            locale_conf="/etc/environment"
-        fi
         ;;
     devuan)
         locale_conf="/etc/default/locale"
         ;;
     ubuntu)
-        os_version=$(cat "${__global}/explorer/os_version")
-        if expr "${os_version}" '>=' 6.10 >/dev/null
-        then
-            # Ubuntu 6.10 (edgy) and later
         locale_conf="/etc/default/locale"
-        else
-            locale_conf="/etc/environment"
-        fi
         ;;
     archlinux)
         locale_conf="/etc/locale.conf"