(PUP-2858) Remove e_parser adapter support

This removes support for the hybrid future parser/old evaluator
by changing the ParserFactory to always select the future parser/
new evaluator combination. As a consequence, the EParserAdapter
is no longer needed and it is now dropped together with its tests.
(PUP-2858) Deprecate the use of Puppet[:environment] == current

This changes defaults.rb to deprecate the use of :environment = :current
The future evaluator is always picked by the Parser::Factory and
the setting has no effect. It may have effect in future versions of
Puppet (for additional experiments when Puppet 4.0 is released). For
that purpose, the settings is not completely removed.
(PUP-2858) Remove use of Puppet[:evaluator] from the code base

This removes all usage of Puppet[:evaluator] from the code base
since it is (in this version) enough to check if Puppet[:parser] is
'future' as the future evaluator is always used.
(PUP-2858) Refactor EvaluatingParser::Transitional to EvaluatingParser

This merges the behavior of the Transitional subclass of the
EvaluatingParser into the main class, as the hybrid solution is no
longer a supported alternative.

As a consequence, all references to the
Pops::Parser::EvaluatingParser::Transitional has been changed to
just Pops::Parser::EvaluatingParser.

This commit alters no behavior.
(PUP-2858) Remove the 3_1 checker and its factory

This removes the Checker_3_1 and its factory from the code base.
This hybrid checker contained less validation (less string) than
the 4.0 checker and its main purpose was to fail expressions that
could not be evaluated with the 3x AST based evaluation (such as -=).

It is also not meaningful to continue its development as the new
4_0 checker is far better. If there is a later need to check
for "backwards compatibility" to 3x, it is better to start fresh with a
new copy of the 4_0 evaluator.
(PUP-2858) Refactor binder to use ne evaluator

The binder always transformed to 3x to get executable code. This
is not needed when using the new evaluator.