Remove unused FlashStep.props.isWebviewShowing

Change-type: patch

lib/gui/app/pages/main/Flash.tsx

@@ -146,7 +146,6 @@ interface FlashStepProps {
 	goToSuccess: () => void;
 	source: SourceOptions;
 	isFlashing: boolean;
-	isWebviewShowing: boolean;
 	style?: React.CSSProperties;
 	// TODO: factorize
 	step: 'decompressing' | 'flashing' | 'verifying';

lib/gui/app/pages/main/MainPage.tsx

@@ -325,7 +325,6 @@ export class MainPage extends React.Component<
 						shouldFlashStepBeDisabled={shouldFlashStepBeDisabled}
 						source={this.state.source}
 						isFlashing={this.state.isFlashing}
-						isWebviewShowing={this.state.isWebviewShowing}
 						step={state.type}
 						percentage={state.percentage}
 						position={state.position}