backend/session: disable libseat examples for subproject by default

We have no use for these.

backend/session/meson.build

@@ -1,7 +1,8 @@
-libseat = dependency('libseat',
+libseat = dependency(
+	'libseat',
 	version: '>=0.2.0',
 	fallback: 'seatd',
-	default_options: ['server=disabled', 'man-pages=disabled'],
+	default_options: ['server=disabled', 'man-pages=disabled', 'examples=disabled'],
 )
 wlr_files += files('session.c')
 wlr_deps += libseat