src/vs/platform/theme/common/iconRegistry.ts/IconRegistry/deregisterIcon
class IconRegistry:	public deregisterIcon(id: string): void {
		delete this.iconsById[id];
		delete this.iconSchema.properties[id];
		const index = this.iconReferenceSchema.enum.indexOf(id);
		if (index !== -1) {
			this.iconReferenceSchema.enum.splice(index, 1);
			this.iconReferenceSchema.enumDescriptions.splice(index, 1);
		}
		this._onDidChange.fire();
	}