Remove redundant synchronized

[kang-hl]

What is the purpose of the change

Remove redundant synchronized

Brief changelog

Verifying this change

Checklist

• Make sure there is a GitHub_issue field for the change (usually before you start working on it). Trivial changes like typos do not require a GitHub issue. Your pull request should address just this issue, without pulling in other changes - one PR resolves one issue.
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[kang-hl]

init()方法的访问修饰符为protected，所以不能将其修改为非同步方法。