dh_ruby: drop remaining mention of rubygems usage check

8 jobs for master in 13 minutes and 53 seconds (queued for 4 seconds)
Status Job ID Name Coverage
  Build
passed #312572
build

00:03:13

 
  Test
passed #312577
autopkgtest

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passed #312578
blhc

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passed #312576
lintian

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passed #312579
piuparts

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passed #312575
reprotest

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passed #312574
test-build-all

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passed #312573
test-build-any

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