revert r1570168, which added a blurb for Unix domain backends

with proxy under the 2.4.8 section

it had already been added the the proper (2.4.7) section


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1583378 13f79535-47bb-0310-9956-ffa450edef68