treewide: Leverage sdbus++-gen-meson

This makes us more consistent with other projects instead of writing
meson builds for sdbus++ by hand.

Change-Id: I38b69bc67b6a3d80cda1b508a76e106a50d8ab93
Signed-off-by: Willam A. Kennington III <wak@google.com>
diff --git a/example/gen/net/meson.build b/example/gen/net/meson.build
new file mode 100644
index 0000000..5ea98c6
--- /dev/null
+++ b/example/gen/net/meson.build
@@ -0,0 +1,2 @@
+# Generated file; do not modify.
+subdir('poettering')