README: Remove "Asynchronous Testing" section
README: Remove "Asynchronous Testing" section

The contents of this section are already covered by Mocha's own documentation

emberjs/ember-mocha,cowboyd/ember-mocha,switchfly/ember-mocha,switchfly/ember-mocha,emberjs/ember-mocha,switchfly/ember-mocha,cowboyd/ember-mocha,cowboyd/ember-mocha