Move snippetClassMap to ConcurrentHashMap.

This in LiftSession, where we were still using a
ConcurrentMap wrapper around ConcurrentHashMap. This
wrapper is now gone, we no longer need ConcurrentMap,
and we can remove some of the hacks needed to support
the name changes it underwent.
Remove webkit_compat.

We no longer need ConcurrentMap, so webkit_compat can
be nuked. Booyan.
Remove extraneous scalaParserVersion variable.