update-report: tweak Cask migration output.

No longer output every cask under the list of changed formulae but
instead create a dedicated, unprinted report section for casks and then
iterate through that instead.

Library/Homebrew/cmd/update-report.rb

@@ -193,7 +193,16 @@ class Reporter
       dst = Pathname.new paths.last
 
       next unless dst.extname == ".rb"
-      next unless paths.any? { |p| tap.formula_file?(p) || tap.cask_file?(p)}
+
+      if paths.any? { |p| tap.cask_file?(p) }
+        # Currently only need to handle Cask deletion/migration.
+        if status == "D"
+          # Have a dedicated report array for deleted casks.
+          @report[:DC] << tap.formula_file_to_name(src)
+        end
+      end
+
+      next unless paths.any? { |p| tap.formula_file?(p) }
 
       case status
       when "A", "D"
@@ -247,12 +256,13 @@ class Reporter
   end
 
   def migrate_tap_migration
-    report[:D].each do |full_name|
+    (report[:D] + report[:DC]).each do |full_name|
       name = full_name.split("/").last
       new_tap_name = tap.tap_migrations[name]
       next if new_tap_name.nil? # skip if not in tap_migrations list.
 
-      if tap == "caskroom/cask"
+      # This means it is a Cask
+      if report[:DC].include? full_name
         next unless (HOMEBREW_REPOSITORY/"Caskroom"/name).exist?
         new_tap = Tap.fetch(new_tap_name)
         new_tap.install unless new_tap.installed?