Remove unused file

docs/DEVELOPER.rst

-Subscription flow
-=================
-
-Happy flow
-----------
-
-Contact1 makes a presence subscription request to contact2.
-
-::
-    <presence type="subscribe" to="contact2@localhost"/>
-
-Contact1 receives a roster update
-
-::
-    <iq type="set" to="contact1@localhost">
-        <query xmlns="jabber:iq:roster">
-            <item jid="contact2@localhost" ask="subscribe" subscription="none"></item>
-        </query>
-    </iq>
-
-Contact2 receives the presence subscription, but no
-roster update. We create a roster item manually in
-handleIncomingSubscription and add the 'requesting'
-property to indicate that this is an incoming request.
-
-Contact2 clicks "Accept". This confirms the
-subscription and subscribes back.
-
-::
-    <presence type="subscribed" to="contact1@localhost"/>
-    <presence type="subscribe" to="contact1@localhost"/>
-
-IF Contact1 is still online and likewise subscribes back, Contact2 will receive a roster update
-
-::
-    <iq type="set" to="contact2@localhost">
-        <query xmlns="jabber:iq:roster">
-            <item jid="contact1@localhost" ask="subscribe" subscription="from"></item>
-        </query>
-    </iq>
-
-ELSE, Contact 2 will receive a roster update (but not an IQ stanza)
-
-::
-    ask = null
-    subscription = "from"
-
-
-Contact1's converse.js client will automatically
-approve.
-
-Contact2 receives a roster update (as does contact1).
-
-::
-    <iq type="set" to="contact2@localhost">
-        <query xmlns="jabber:iq:roster">
-            <item jid="contact1@localhost" subscription="both"></item>
-        </query>
-    </iq>