Revert "build: undef WITH_JANSSON for SETUID_RPC_CLIENT"

This reverts commit 93fdc9e0.

Jansson cannot parse QEMU's quirky JSON.
Revert back to yajl.

https://bugzilla.redhat.com/show_bug.cgi?id=1614569Signed-off-by: NJán Tomko <jtomko@redhat.com>
Reviewed-by: NDaniel P. Berrangé <berrange@redhat.com>

config-post.h

@@ -36,7 +36,6 @@
 # undef WITH_DEVMAPPER
 # undef WITH_DTRACE_PROBES
 # undef WITH_GNUTLS
-# undef WITH_JANSSON
 # undef WITH_LIBSSH
 # undef WITH_MACVTAP
 # undef WITH_NUMACTL