configure: Don't add Xen's libs to LDFLAGS

When Xen is detected via pkg-config, it isn't necessary to modify
LDFLAGS as modifying libs_softmmu is enough.
Reported-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>
Signed-off-by: NAnthony PERARD <anthony.perard@citrix.com>
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NMichael Tokarev <mjt@tls.msk.ru>
Reviewed-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>

configure

@@ -2359,7 +2359,6 @@ if test "$xen" != "no" ; then
     fi
     QEMU_CFLAGS="$QEMU_CFLAGS $($pkg_config --cflags $xen_pc)"
     libs_softmmu="$($pkg_config --libs $xen_pc) $libs_softmmu"
-    LDFLAGS="$($pkg_config --libs $xen_pc) $LDFLAGS"
   else
 
     xen_libs="-lxenstore -lxenctrl -lxenguest"