Removing bug report specs

Removed almost all bug report specs per #400, except for one, `bug_report_8165_spec.rb`. Reading what's commented there by @dchelimsky it says that the fix was to keep track of whether respond_to? has been proxied. Going to the Proxy class and removing the instance variable `@already_proxied_respond_to` doesn't break any specs, not even the ones in the bug report. So this may be the case for dropping the bug_report file AND keep an eye on that attribute?