As of -3 (debian revision 3) the javadocs are installed to

/usr/share/i2p/docs/javadoc and /usr/share/doc/i2p-doc/api is a symbolic link
to this location. To ensure the link can be created, we check to see if
/usr/share/doc/i2p-doc/api is a folder. If it is, it gets removed.

debian/i2p-doc.preinst

@@ -6,6 +6,10 @@ if [ ! -z $2 ]; then
                 test -d /usr/share/doc/i2p-doc \
                         && rm -rf /usr/share/doc/i2p-doc
         fi
+	if dpkg --compare-versions $2 lt 0.8.7-3; then
+                test -d /usr/share/doc/i2p-doc/api \
+                        && rm -rf /usr/share/doc/i2p-doc/api
+        fi
 fi
 
 #DEBHELPER#