This reverts commit a01de4a7.

* Add missing generators feature flags

* Generate files

* Add generators flags

* fixup! Add generators flags

Fixes #779

Signed-off-by: Rick Waldron <waldron.rick@gmail.com>

* Add tests for prototype realm inference

* Add tests for miscellaneous realm concerns

* Add tests for realm of spec-created Errors

In some cases, Error objects produced by the specification are
observable from ECMAScript code. Among these cases, some are further
differentiated in that they occur outside of any built-in function and
may be triggered through syntactic production directly. The current
realm record is commonly interpreted incorrectly under these
circumstances.

Add tests asserting that the expected realm record is used when
constructing such Error objects.

* Add tests for realm use in ArraySpeciesCreate

* Add tests for function realm retrieval

* Add tests for cross-realm behaviors of Symbols

* Add tests for GetValue and PutValue

* Add tests for realm of spec-created Arrays

In some cases, Arrays produced by CreateArrayFromList are observable
from ECMAScript code. Among these cases, two occur outside of any
built-in function and may be triggered through syntactic production
directly. The current realm record is commonly interpreted incorrectly
under these circumstances.

Add tests asserting that the expected realm record is used when
constructing arrays.

* Add test for spec-created object

* fixup! Add tests for realm of spec-created Errors

* fixup! Add tests for realm of spec-created Errors

* fixup! Add tests for prototype realm inference

* fixup! Add tests for miscellaneous realm concerns

* Improve tests for GeneratorPrototype methods

- Assert return values more consistently
- Expand tests for constraints on `this` value

* Add more tests for dynamic GeneratorFunctions

* Add more tests for GenerationFunction.prototype

* Add more tests for the GeneratorFunction object

* Extend test: GeneratorFunction.prototype.prototype

* Improve precision of tests for generator methods

Extend existing assertions to explicitly verify that execution halts at
the intended location. Correct tests which were previously asserting
this behavior in contexts that did not match their name/description.

* Remove unused variables

* fixup! Improve tests for GeneratorPrototype methods

* fixup! Improve tests for GeneratorPrototype methods

This change set includes tests for most invocations of the
SetFunctionName abstract operation in the ES2015 specification.
Practical testing considerations preclude the introduction of tests for
certain invocations:

- The project is still vetting methods to sustainably test the semantics
  of the Destructuring Binding pattern across all valid productions.
  - 13.3.3.6 Runtime Semantics: IteratorBindingInitialization
  - 13.3.3.7 Runtime Semantics: KeyedBindingInitialization
- Without a loader, there is no way to access a function object declared
  in an ExportDeclaration, so `name` assignment cannot be tested in
  these cases
  - 14.1.19 Runtime Semantics: InstantiateFunctionObject
  - 14.4.12 Runtime Semantics: InstantiateFunctionObject
  - 14.5.15 Runtime Semantics: BindingClassDeclarationEvaluation
  - 15.2.3.11 Runtime Semantics: Evaluation

The `test/language/generators/` directory contained a single file that
concerned generators derived both from syntactic form and from a
built-in function.

Refactor this test into two files and place each in the appropriate
directory.

These tests are derived from the following files within the Google V8
project:

    test/mjsunit/es6/generators-iteration.js
    test/mjsunit/es6/generators-objects.js
    test/mjsunit/es6/generators-runtime.js
    test/mjsunit/es6/generators-states.js