Remove ess-R-object-popup from ess layer.

As described in issue #9464, this package was removed from melpa for
not having a GPL compatible license and is causing an error every time
spacemacs starts.

Author: ISELECT1\naylyn.gaffney

layers/+lang/ess/packages.el

@@ -13,7 +13,6 @@
   '(
     ess
     ess-R-data-view
-    ess-R-object-popup
     ess-smart-equals
     golden-ratio
     org))