Fix memory leak for 'error' on session during h2 requests

[timostamm]

Fixes #725 by removing the event listener completely. All session events are handled by the Http2SessionManager since #673, and I can't think of a reason we would need it here.

The reproduction for the leak from #725 (comment) passes now:

$ node -v
v18.17.0
$ node --trace-warnings repro-725.mjs
req 0
req 1
req 2
req 3
req 4
req 5
req 6
req 7
req 8
req 9
req 10
req 11