Revert Joshua Kwan's patch committed 11 Sep 2009.

Some systems poll function sets POLLHUP in revents without setting
POLLIN, and sets POLLERR without setting POLLIN and POLLOUT. In some
libcurl code execution paths this could trigger busy wait loops with
high CPU usage until a timeout condition aborted the loop.

The reverted patch addressed the above issue for a very specific case,
when awaiting c-ares to resolve. A libcurl-wide fix superceeds this one.

http://cool.haxx.se/cvs.cgi/curl/lib/select.c.diff?r1=1.52&r2=1.53