bugdown: Remove ERROR_BOT markdown rendering notices.

Nobody has used this feature in years, and it causes certain types of
markdown issues in development to completely DoS the development
environment by making it possible for the "Bugdown timeout" exception
handler to timeout in bugdown.

Since we already send an email to the server administrators, there's
no need to replace this feature with anything.

zerver/lib/bugdown/__init__.py

@@ -1657,13 +1657,10 @@ def do_convert(content, message=None, message_realm=None, possible_words=None, s
         log_bugdown_error('Exception in Markdown parser: %sInput (sanitized) was: %s'
                           % (traceback.format_exc(), cleaned))
         subject = "Markdown parser failure on %s" % (platform.node(),)
-        if settings.ERROR_BOT is not None:
-            error_bot_realm = get_system_bot(settings.ERROR_BOT).realm
-            internal_send_message(error_bot_realm, settings.ERROR_BOT, "stream",
-                                  "errors", subject, "Markdown parser failed, email sent with details.")
         mail.mail_admins(
             subject, "Failed message: %s\n\n%s\n\n" % (cleaned, traceback.format_exc()),
             fail_silently=False)
+
         raise BugdownRenderingException()
     finally:
         current_message = None