Re-working the fix for http://issues.apache.org/bugzilla/show_bug.cgi?id=56653

I rollback addition of HostMapping class (reverting most of r1604319)
I will work on an alternative solution that should be easier to backport to Tomcat 7.

(This revert temporarily breaks support for Aliases, per comment 2 in BZ 56653. The alternative solution will fix it.)

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1604934 13f79535-47bb-0310-9956-ffa450edef68