docs: Don’t install object manager example separately
The relevant parts of the generated example documentation are already
xi:include
d into the migrating-gdbus.xml
page, so are turned into
HTML there. Installing them separately means they also get installed
into /usr/share/gtk-doc/html/gdbus-object-manager-example/
, which
seems redundant.
Signed-off-by: Philip Withnall withnall@endlessm.com