src: remove `Environment::tracing_agent_writer()`

As per the conversation in https://github.com/nodejs/node/issues/22513,
this is essentially global, and adding this on the Environment
is generally just confusing.

Refs: https://github.com/nodejs/node/issues/22513
Fixes: https://github.com/nodejs/node/issues/22767

PR-URL: https://github.com/nodejs/node/pull/23781


Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Matheus Marchini <mat@mmarchini.me>