Revert usage string change from r22930.

Amiconn: "langv2" had nothing to do with the language version byte in the
generated .lng file, so "langv4" makes no sense. It refers to the format of the
.lang. The current, tag-based format which allows to restrict strings to
certain targets or features is called langv2 versus the old, simpler format.


git-svn-id: svn://svn.rockbox.org/rockbox/trunk@22939 a1c6a512-1295-4272-9138-f99709370657

tools/genlang

@@ -28,7 +28,7 @@ my %user2num =
 
 if(!$ARGV[0]) {
     print <<MOO
-Usage: genlang [options] <langv4 file>
+Usage: genlang [options] <langv2 file>
 
  -p=<prefix>
     Make the tool create a [prefix].c and [prefix].h file.