Do not print field keys

They are already contained within the fetched string.

dotfiles/imapfilter/common/functions.lua

 function _notifirc1(subj, from, body)
     --notify about message using (pre-configured) notifirc
     local fd = assert(io.popen('notifirc -f - "message preview:"', "w"))
-    local fmt = "> Subject: %s\n> From: %s\n> Body: %s"
+    local fmt = "> %s\n> %s\n> BODY: %s"
     fd:write(fmt:format(subj, from, body))
     fd:close()
 end