Revert "Remove EMF Parsley from Modeling package"

EMF Parsley is available from the 2018-09 RC2 build of the Simultaneous
Release again.

This reverts commit 5a11a063d08399df3dfed8c7135ce6d15a42b363.
diff --git a/packages/org.eclipse.epp.package.modeling.product/epp.product b/packages/org.eclipse.epp.package.modeling.product/epp.product
index 41d10c4..90db148 100644
--- a/packages/org.eclipse.epp.package.modeling.product/epp.product
+++ b/packages/org.eclipse.epp.package.modeling.product/epp.product
@@ -209,10 +209,8 @@
       <feature id="org.eclipse.emf.ecoretools.explorer.contextual" installMode="root"/>
       <feature id="org.eclipse.emf.ecoretools.design" installMode="root"/>
       <feature id="org.eclipse.emf.ecp.sdk.feature" installMode="root"/>
-      <!-- not available in 2018-09 RC1
       <feature id="org.eclipse.emf.parsley.sdk" installMode="root"/>
       <feature id="org.eclipse.emf.parsley.sdk.source" installMode="root"/>
-      -->
       <feature id="org.eclipse.emf.emfstore.sdk.feature" installMode="root"/>
       <feature id="org.eclipse.emf.query.sdk" installMode="root"/>
       <feature id="org.eclipse.emf.sdk" installMode="root"/>