[Console] Minor perf improvement

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

It's useless to set the command application if a command is not enabled
@KingCrunch I thought like you and I just saw the PR https://github.com/symfony/symfony/pull/1470, so we can remove this line safety :)