Call dissociate_reader in rmw_destroy_subscription

[eboasson]

A call to dissociate_writer, like it did before, is a no-op. The result
is that the ros_discovery_info topic sample keeps growing when one
creates and destroy subscriptions in the application.

Signed-off-by: Erik Boasson eb@ilities.com

[omertal88]

Hello,

This PR solves an issue I'm experiencing where I occasionally replacing my subscribers with others. This over time accumulates until the message sent to ros_discovery_info is too big to be sent. At that point my network traffic will sky rocket, as the other peer keeps requesting that sample, and the sender peer can't fully send it.
I would highly appreciate if this can get cherry-picked into the upcoming galactic release.

Thank you.
Omer

[eboasson]

Thanks @omertal88 for reviewing it. It seems silly to run the full CI for this change, so below are the badges for a run with just test_rmw_implementation and test_rclcpp as a sanity check:

• Linux
• Linux-aarch64
• Windows