ARROW-6679: [RELEASE] Remove (temporarily, hopefully) the autobrew scripts

[nealrichardson]

Once an appropriate license is supplied upstream, we can hopefully just revert this commit.

[wesm]

+1, thanks for addressing this quickly

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@a89c803). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #5495   +/-   ##
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  Coverage          ?   77.13%           
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  Files             ?       58           
  Lines             ?     4002           
  Branches          ?        0           
=========================================
  Hits              ?     3087           
  Misses            ?      915           
  Partials          ?        0

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[nealrichardson]

Autobrew got a license file, so closing this in favor of #5501