Revert "Mobile: Fixes #2847: Fixed text issue in config screen on some devices (#2851)"

Reverted to fix regression (crash) in iOS app.

https://github.com/laurent22/joplin/pull/2851#issuecomment-610688103

This reverts commit e024015d5e.

ReactNativeClient/lib/components/global-style.js

@@ -89,7 +89,6 @@ function addExtraStyles(style) {
 		color: style.color,
 		fontSize: style.fontSize * 1.2,
 		fontWeight: 'bold',
-		fontFamily: 'Roboto',
 	};
 
 	style.headerWrapperStyle = {

ReactNativeClient/lib/components/screens/config.js

@@ -242,7 +242,6 @@ class ConfigScreenComponent extends BaseScreenComponent {
 		styles.linkText.borderBottomColor = theme.color;
 		styles.linkText.flex = 0;
 		styles.linkText.fontWeight = 'normal';
-		styles.linkText.fontFamily = 'Roboto';
 
 		styles.headerWrapperStyle = Object.assign({}, styles.settingContainer, theme.headerWrapperStyle);