bug #16050 [TwigBundle] fix useless and failing test (Tobion)

This PR was merged into the 2.3 branch.

Discussion
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[TwigBundle] fix useless and failing test

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | n/a

This test is failing in php 7, see https://travis-ci.org/symfony/symfony/jobs/83107755#L2015
But it also doesn't test anything. So it's useless in it's current form.

In 2.7 we have more tests that are actually useful. So the class is not untested.

Commits
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d94dd16 [TwigBundle] fix useless and failing test