renderer: Do not capture 'this' pointer in lambdas.

In Vala, 'this' pointer is captures in lambdas by default. This causes issues
with a buggy C code, which depends on the order of object destruction (e.g.
AVTransport is destroyed much later than the rest of services, causing it to
use already-freed objects).

Signed-off-by: Milan Plzik <milan.plzik@streamunlimited.com>