…19459)

The tcp and unix input sources were leaking references causing a memory leak.
When an accepted connection ended inputsource/common.Closer was
supposed to delete the pointer that it held to the connection, but due to a code
error `delete` was being called on the wrong map.

Instead of modifying the common.Closer I replaced it with a cancellable context.Context which
is designed to propagate signals from parent to children and requires less code.

(cherry picked from commit 61f4846)