Remove brew-mirror-check command

This command uses removed API and is thus broken. It can always be
retrieved from the git history.

Library/Contributions/cmd/brew-mirror-check.rb

@@ -1,52 +0,0 @@
-require 'formula'
-
-class Formula
-  def test_mirror mirror
-    # Checksum verification is done against @active_spec, so we need only
-    # populate the stub spec object with the mirror URL.
-    spec = SoftwareSpec.new(mirror)
-    downloader = download_strategy.new(name, spec)
-
-    # Force the downloader to attempt the download by removing the tarball if
-    # it is allready cached.
-    cached_download.unlink if cached_download.exist?
-
-    downloader.fetch
-  rescue StandardError
-    opoo "Failed to fetch from URL: #{url}"
-  else
-    verify_download_integrity(cached_download) if cached_download.file?
-  end
-end
-
-module Homebrew extend self
-  def check_mirrors
-    mirror_check_usage = <<-EOS
-Usage: brew mirror-check <formulae ...>
-
-Cycle through mirror lists for each formula, attempt a download and validate file hashes.
-    EOS
-
-    if ARGV.empty?
-      puts mirror_check_usage
-      exit 0
-    end
-
-    formulae = ARGV.formulae
-    raise FormulaUnspecifiedError if formulae.empty?
-
-    formulae.each do |f|
-      if f.mirrors.empty?
-        opoo "#{f.name} has no mirrors"
-        next
-      else
-        oh1 "Testing mirrors for #{f.name}"
-        f.mirrors.each{ |m| f.test_mirror m }
-      end
-    end
-  end
-end
-
-# Here is the actual code that gets run when `brew` loads this external
-# command.
-Homebrew.check_mirrors