rewriteutil: remove now-unused `update` argument from `rewite()`

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branch : stable
8 jobs for topic/stable/touch-merge-fix in 7 minutes (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed checks-py2 #227364

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passed checks-py3 #227365

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passed doc #227370

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manual pytype #227363
allowed to fail manual
passed tests-py2-cext #227366

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passed tests-py2-pure #227367

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passed tests-py3-cext #227368

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passed tests-py3-pure #227369

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