Revert "test-bot: better xml character filtering"

This reverts commit 7032591bd44a8f50aaa55574ac97cd5cb7261460 and
commit 946c6deb4b5168ad2ec15e62aa6e81181e9e246c.

Library/Homebrew/cmd/test-bot.rb

@@ -917,11 +917,8 @@ module Homebrew
           testcase.add_attribute "time", step.time
 
           if step.has_output?
-            # Remove invalid XML characters
-            # http://www.w3.org/TR/xml/#charsets
-            output = step.output
-            output.force_encoding("UTF-8") if output.respond_to?(:force_encoding)
-            output.gsub!(/[^\x09\x0A\x0D\x20-\uD7FF\uE000-\uFFFD\u10000-\u10FFFF]/, "")
+            # Remove invalid XML CData characters from step output.
+            output = step.output.delete("\000\a\b\e\f\x2\x1f")
 
             if output.bytesize > BYTES_IN_1_MEGABYTE
               output = "truncated output to 1MB:\n" \