Netwarep proxy makefiles

- remove unneeded XINCDIRS
  - there are no header files in $(STDMOD)/http
  - $(STDMOD)/generators and $(STDMOD)/ssl
    for serf were likely copy&paste from
    NWGNUproxy, but serf doesn't need them
  - $(STDMOD)/proxy for wstunnel likely
    copy&paste from some lb module but
    wstunnel doesn't need them


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1728812 13f79535-47bb-0310-9956-ffa450edef68