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

8 jobs for topic/default/touch-merge-fix in 5 minutes and 41 seconds (queued for 1 second)
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  Test
passed #110386
checks-py2

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passed #110387
checks-py3

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passed #110392
doc

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manual #110385
allowed to fail manual
pytype
passed #110388
tests-py2-cext

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passed #110389
tests-py2-pure

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passed #110390
tests-py3-cext

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passed #110391
tests-py3-pure

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