src/vs/workbench/contrib/terminal/browser/terminalGroupService.ts/TerminalGroupService/unsplitInstance
class TerminalGroupService:	unsplitInstance(instance: ITerminalInstance) {
		const oldGroup = this.getGroupForInstance(instance);
		if (!oldGroup || oldGroup.terminalInstances.length < 2) {
			return;
		}

		oldGroup.removeInstance(instance);
		this.createGroup(instance);
	}