package/neon: properly enable expat

package/neon: properly enable expat

Currently, we forcibly tell neon's configure where to look for libexpat.
This means that neon does not search for it, and consequently forgets to
add -lexpat as its Libs.Private in its .pc file. As thus, a static link
against neon forgets to pull in -lexpat (it works for a dynamic link
because libneon has a NEEDED on libexpat).

The reason for specifying the explicit path in this case is lost to
history; neon's configure can correctly find libexpat nowadays.

Fixes:
    http://autobuild.buildroot.org/results/884/884746351fc47f4ad19fb3fda7c5e0ee85fcff15/
    http://autobuild.buildroot.org/results/0c5/0c584522c26640e29980150a87a5b5d8c02e5f8b/

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>