Remove protected fields from ResourceManager and ResourceSet
Remove protected fields from ResourceManager and ResourceSet

Fixes https://github.com/dotnet/standard/issues/36

The protected fields on ResourceManager and ResourceSet don't have
any real usage and cause some dependencies (in particular HashTable)
that we would like to break in some platforms so removing them from
netstandard.

weshaggard/standard,ericstj/standard,ericstj/standard,weshaggard/standard