software/caddy-frontend: don't install caucase eggs twice

If we list eggs as eggs= of a zc.recipe.egg section, the scripts of these eggs
will be installed again.

This fixes this error while building:

    While:
      Installing extra-eggs.
    Error: The following paths are already installed by other sections: {'/srv/slapgrid/slappart8/srv/testnode/cvt/inst/test0-0/tmp/soft/72b4c4e0472506664a0cb3cc44bbb0b2/bin/caucased-manage': 'caucase-eggs', '/srv/slapgrid/slappart8/srv/testnode/cvt/inst/test0-0/tmp/soft/72b4c4e0472506664a0cb3cc44bbb0b2/bin/caucase-key-id': 'caucase-eggs', '/srv/slapgrid/slappart8/srv/testnode/cvt/inst/test0-0/tmp/soft/72b4c4e0472506664a0cb3cc44bbb0b2/bin/caucase-updater': 'caucase-eggs', '/srv/slapgrid/slappart8/srv/testnode/cvt/inst/test0-0/tmp/soft/72b4c4e0472506664a0cb3cc44bbb0b2/bin/caucase-rerequest': 'caucase-eggs', '/srv/slapgrid/slappart8/srv/testnode/cvt/inst/test0-0/tmp/soft/72b4c4e0472506664a0cb3cc44bbb0b2/bin/caucase': 'caucase-eggs', '/srv/slapgrid/slappart8/srv/testnode/cvt/inst/test0-0/tmp/soft/72b4c4e0472506664a0cb3cc44bbb0b2/bin/caucase-probe': 'caucase-eggs', '/srv/slapgrid/slappart8/srv/testnode/cvt/inst/test0-0/tmp/soft/72b4c4e0472506664a0cb3cc44bbb0b2/bin/caucased': 'caucase-eggs'}

software/caddy-frontend/common.cfg

@@ -16,6 +16,7 @@ extends =
   ../../stack/monitor/buildout.cfg
 
 parts +=
+  caucase-eggs
   template
   template-caddy-frontend
   template-caddy-replicate
@@ -78,7 +79,6 @@ eggs =
 eggs +=
   websockify
   erp5.util
-  ${caucase-eggs:eggs}
   collective.recipe.shelloutput
 
 [template-common]