Static fields were broken up from instance fields and demoted to
Stage 2 in the November 2017 TC39 meeting. This patch removes the
test262 tests which test static class fields.

BigInt.parseInt will be removed in
https://github.com/tc39/proposal-bigint/pull/101

This patch removes the associated test262 tests.

The `groups` property must be created unconditionally. https://github.com/tc39/proposal-regexp-named-groups/pull/40

The use of `let` is unnecessary here, particularly in a
file that is needed to run any of the tests, even the ES5 tests.
Removing it allows older engines to run older tests.

Refactor AssignmentExpression tests for parsers

Correct metadata reference in "contributing" docs