remove duplicate variables from config

remove duplicate variables from config

... because they are already in Paths.mk:
BINDIR, LIBEXEC, PRIVATE_BINDIR, PRIVATE_PREFIX, SBINDIR, SHAREDIR,
XEN_CONFIG_DIR, XENFIRMWAREDIR, XEN_LOCK_DIR, XEN_PAGING_DIR,
XEN_RUN_DIR. Remove unused PKG_XEN_PREFIX, which was also incorrectly
assigned to PRIVATE_PREFIX.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: Ian Jackson <ian.jackson@eu.citrix.com>
Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Cc: Wei Liu <wei.liu2@citrix.com>
[ ijc -- ran autogen.sh as requested ]