Remove Windows icons

Discourages Windows usage.

_includes/sections/email-clients.html

@@ -7,7 +7,6 @@ description="Thunderbird is a free, open source, cross-platform email, newsgroup
 website="https://www.thunderbird.net/"
 forum="https://forum.privacytools.io/t/discussion-thunderbird/659"
 source="https://hg.mozilla.org/comm-central/"
-windows=""
 mac=""
 linux=""
 bsd=""
@@ -20,7 +19,6 @@ description="Claws Mail is a free and open source, GTK-based email and news clie
 website="https://www.claws-mail.org/"
 forum="https://forum.privacytools.io/t/discussion-claws-mail/660"
 git="https://git.claws-mail.org/"
-windows=""
 mac=""
 linux=""
 bsd=""