(PUP-3449) Skip merging node parameters reserved in top scope

So I think I've come full circle on this issue and am no longer convinced we should be preventing the scope from raising an error if it is presented with 'trusted' or 'facts' in the node parameters.  But this potentially conflicts with how PuppetDB is storing 'trusted'.  If you setup your master to work with PuppetDB and do not set a separate cache, you will stop compiling.  Perhaps this is seen as an invalid configuration, but it seems odd to me.