fix: time-picker bug

[zkwolf]

当使用backspace删除所有字符后，输入第一个字符控制台报错，并无字符显示

问题在于尝试在子组件改变prop showStr，但是并没有发现这个showStr实际带来了什么作用，目前方案是直接删除了，按照例子测试了一下，暂时没有发现副作用

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   time-picker bug when use backspace to clear input #1173

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[codecov]

Codecov Report

Merging #1176 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master   #1176   +/-   ##
======================================
  Coverage    87.1%   87.1%           
======================================
  Files         146     146           
  Lines        4847    4847           
  Branches     1453    1453           
======================================
  Hits         4222    4222           
  Misses        558     558           
  Partials       67      67

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This pull request has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.