GH-421: Cleaned up the _Output_ channel UI.

- Merged the Arduino channels into one,
 - Removed the channel selector dropdown from the UI.

Closes arduino/arduino-pro-ide#421.

Signed-off-by: Akos Kitta <kittaakos@typefox.io>

arduino-ide-extension/src/common/protocol/output-service.ts

@@ -1,5 +1,4 @@
 export interface OutputMessage {
-    readonly name: string;
     readonly chunk: string;
     readonly severity?: 'error' | 'warning' | 'info'; // Currently not used!
 }