Remvoe AP_END_OF_BRIGADE. This definition didn't really mean anything,

Remvoe AP_END_OF_BRIGADE.  This definition didn't really mean anything,
because it didn't signify the end of the brigade, and it didn't signify
the end of a response.  It ended up meaning flush the data, which can be
detemined with bucket type checks.  This also makes the FLUSH and EOS
buckets have a 0 length, which makes a lot of code cleaner, because now we
can just add lengths and be sure they are all >=0.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@86851 13f79535-47bb-0310-9956-ffa450edef68