Remove remaining usage message duplication between ECJ and AJC

Remove remaining usage message duplication between ECJ and AJC

The resource key 'misc.usage' is completely gone from
.../jdt/internal/compiler/batch/messages_aspectj.properties. Instead,
JDT Core was adjusted in such a way as to patch the new resource key
'misc.usage.aspectj' into the upstream 'misc.usage' in the right place.

Now finally the properties file is as lean as I envisioned it to be,
without any loss of information and without the need of future manual
synchronisation of duplicate texts for every release.

At the same time, usage text detection in AjdtCommand::inferKind was
improved and also adjusted to the new situation.

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>