Translation docs update: don't recommend 20-year-old gettext; use msginit

Warning about gettext versions earlier than 0.10.35 is pointless,
as even 0.10.35 is from 2001, and so old it isn't even available
on GNU mirrors anymore. We shall not recommend a specific version in
the first place.

The proper way to start a new translation is to use msginit to initialize
a .po file -- just copying the .pot leaves many fields to their default
values, which the translator would need to fill in manually (the
Plural-Forms: field in particular).

docs/contributing/translators-guide.md

@@ -5,10 +5,9 @@ This note is addressed to wxWidgets translators.
 
 First of all, here is what you will need:
 
-1. GNU gettext package version 0.10.35 or later (NB: earlier versions were
-   known to have serious bugs)
+1. GNU gettext package
 
-   a) for Unix systems you can download gettext-0.10.tar.gz from any GNU
+   a) for Unix systems you can download gettext-0.xx.yy.tar.gz from any GNU
       mirror (RPMs and DEBs are also available from the usual places)
 
    b) for Windows you can download the precompiled binaries from