(PUP-3268) Remove file watching from environment

File watching for files loaded through the environment was only being
done for legacy environments. Now that legacy environments have been
removed, the file watching code in Node::Environment,
Resource::TypeCollection, and the E4ParserAdapter goes away as well.

The Directories environment loader no longer needs to turn off file
watching for directory environments.

There is still an Environment#check_for_reparse method which tests if
the Puppet[:code] has changed or last parse of the environment failed.
It is called by the resource_type/parser indirector, the parser face and
the parser/compiler, and may no longer be necessary.