(PUP-3370) Remove serialization support from indirector request

Support for serializing/deserializing indirector requests was added per
Redmine issue #7080, but was never fully fleshed out and is a rather
sketchy idea in the first place. This commit removes all serialization
logic from Puppet::Indirector::Request.
(PUP-3277) Use classifier when testing enc response

The current test sets up an enc instance for foss, but when running
against pe, it fails because the pe node_terminus configuration is in
[master] not [main].  We could adjust that, but then we
are not testing against a real PE environment, so instead, use the
classifier.
Merge branch 'issue/master/pup-3277-enc-non-existent-directory-environment-test-uses-classifier-in-pe'

* issue/master/pup-3277-enc-non-existent-directory-environment-test-uses-classifier-in-pe:
  (PUP-3277) Use classifier when testing enc response
(PUP-3300) Remove extend self from Checksums

This commit modifies Puppet::Util::Checksums to not extend self anymore
to move to using module_function.
(PUP-3289) Remove deprecated catalog_format and dynamicfacts settings

This commit is part of the Puppet 4 code removal effort.
Merge remote-tracking branch 'upstream/pr/3230'

* upstream/pr/3230:
  (PUP-3370) Remove serialization support from indirector request
Merge pull request #3232 from whopper/pup-3289/removal/cat_format-dynfacts

(PUP-3289) Remove deprecated catalog_format and dynamicfacts settings
Merge pull request #3231 from demophoon/refactor/master/pup-3300-checksum-refactor

(PUP-3300) Remove extend self from Checksums
(maint) Remove support for OSX versions <= 10.6