Remove incorrect assertions

[ef4]

If you use render on a component and then call this.set, you get an assertion:

'You cannot call this.set when passing a component to render() (the rendered component does not have access to the test context).',

But that's not true and hasn't been since the introduction of components with access to lexical scope. For example:

let self = this;
render(<template>{{self.message}}</template>)
this.set('message', 'updated')

My example uses a workaround for emberjs/babel-plugin-ember-template-compilation#61, but we have open PRs fixing that issue in which case this would also just work directly:

render(<template>{{this.message}}</template>)
this.set('message', 'updated')

Critically, @embroider/template-tag-codemod can produce these situations entirely automatically, as it upgrades any existing tests to template tag. So whether you think it's good for new code to use this.set in tests, as we codemod all templates to template tag, existing tests that use this.set are going to hit this assertion unnecessarily.