Make the debug_session.error telemetry event capture only debugging errors, not regular debug exit

[luabud]

[kimadeline]

On regular exit the onError handler is triggered with the following error:

message:'read error'
stack: 'Error: read error
at Socket. (/Applications/Visual Studio Code.app/Contents/Resources/app/out/vs/workbench/services/extensions/node/extensionHostProcess.js:90:2066)
at Socket.emit (events.js:327:22)
at Pipe. (net.js:673:12)
at Pipe.callbackTrampoline (internal/async_hooks.js:131:14)'

Need to figure out how to not receive this error, or if it's safe to ignore it.

[eleanorjboyd]

@luabud could you elaborate on this? Wondering if this still applies since the move to the separate debug extension