src/vs/platform/remote/common/tunnel.ts/AbstractTunnelService/closeTunnel
class AbstractTunnelService:	async closeTunnel(remoteHost: string, remotePort: number): Promise<void> {
		this.logService.trace(`ForwardedPorts: (TunnelService) close request for ${remoteHost}:${remotePort} `);
		const portMap = this._tunnels.get(remoteHost);
		if (portMap && portMap.has(remotePort)) {
			const value = portMap.get(remotePort)!;
			value.refcount = 0;
			await this.tryDisposeTunnel(remoteHost, remotePort, value);
		}
	}