[Build] Fix small typo in the summary at the end of configure.ac

Signed-off-by: Emanuele Aina <emanuele.aina@collabora.com>
[Build] Ship the internal library in a private directory

The libdleyna-server-1.0.so library is not really meant for public
consumption and it's just an internal implementation detail.

To prevent any confusion, ship it in a package-specific subdirectory of
the configured libdir.

Signed-off-by: Emanuele Aina <emanuele.aina@collabora.com>