chore: remove ssh background config

[fioan89]

From my testing, Toolbox forwards through SSH (i.e. through Coder) a remote port associated with the IDE
running in server mode, to localhost in order for the server (i.e. the remote IDE) to communicate with
JBClient. Unlike with Gateway, Toolbox manages to reuse the SSH connection, and it doesn't open a separate
one for port forwarding.

From Gateway we inherited two ssh hostnames per each workspace, one for background connections that did not
involve running IDEs. Coder discards the bg. connection from the collected metrics in order to
avoid double counting. Since Toolbox manages to re-use the connection we don't need to worry
about double counting.

For this particular change, I deployed the latest Coder version with prometheus metrics and experiments
enabled (i.e. --prometheus-enable --prometheus-collect-agent-stats --experiments=workspace-usage) and made the following experiment:

1. Opened up Toolbox, logged into Coder. At this point:

• agent_sessions_total and coderd_agentstats_session_count_jetbrains were missing from prometheus metrics
• jetbrains session count from api/v2/deployment/stats showed 0

2. Opened up a Workspace at which point Toolbox established the SSH connection:

• agent_sessions_total and coderd_agentstats_session_count_jetbrains increased to 1
• jetbrains session count from api/v2/deployment/stats increased to 1 as well

3. Hit the install button on RustRover, everything stayed unchanged

4. Open RustRover, nothing changes in the stats.

[code-asher]

Great news on Toolbox using a single connection!

I tried running Toolbox 2.6.1 on my Windows VM (for some reason I cannot seem to get it running on Linux) but I keep getting "exit code: 7" and blank stderr, so I have not been able to test, but the code change looks good to me.

[fioan89]

I'll have to get my hands on Windows machine/VM, honestly I only tested on macOS.