Silence deprecation warnings during formatter specs.

The specs are demonstrating usage of `pending`,
which always generates a warning on 2.99.
Address warning.

warning: instance variable @show_failures_in_pending_blocks not initialized
Deprecate example group aliasing methods.

These methods are available off of config, which
is the public API we want.
Merge pull request #1412 from rspec/deprecate-example-group-alias-methods

Deprecate example group alias methods