refactor: remove always falsy condition on perf

[clarkdo]

Signed-off-by: Clark Du [email protected]

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change? (check one)

• Yes
• No

If yes, please describe the impact and migration path for existing applications:

The PR fulfills these requirements:

• It's submitted to the dev branch for v2.x (or to a previous version branch), not the master branch
• When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)
• All tests are passing: https://github.com/vuejs/vue/blob/dev/.github/CONTRIBUTING.md#development-setup
• New/updated tests are included

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature (to avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it)

Other information:

1. perf will never be null or undefined due to previous definition, so remove the block
2. even if perf is null or undefined, the block will throw and Cannot read property error

[JounQin]

perf && seems also useless.

[clarkdo]

@JounQin
get it, will make some changes

[clarkdo]

@JounQin
done, thanks