unread: Move a UI-specific helper to the appropriate bit of UI.

This is basically part of the UI logic; it's a choice for how to
represent this information visually.  Move it to the relevant spot
of our UI code.

Then as a bonus, inline it and use that to simplify the logic.

src/common/UnreadCount.js

@@ -4,7 +4,6 @@ import { StyleSheet, Text, View } from 'react-native';
 import type { ViewStyleProp } from 'react-native/Libraries/StyleSheet/StyleSheet';
 
 import { BRAND_COLOR } from '../styles';
-import { unreadToLimitedCount } from '../utils/unread';
 import { foregroundColorFromBackground } from '../utils/color';
 
 const styles = StyleSheet.create({
@@ -83,10 +82,11 @@ export default class UnreadCount extends PureComponent<Props> {
     const textColor = foregroundColorFromBackground(color);
     const textStyle = [styles.text, inverse && styles.textInverse, { color: textColor }];
 
+    const countString = limited && count >= 100 ? '99+' : count.toString();
     return (
       <View style={frameStyle}>
         <Text style={textStyle} numberOfLines={1}>
-          {limited ? unreadToLimitedCount(count) : count}
+          {countString}
         </Text>
       </View>
     );

src/utils/unread.js

@@ -15,6 +15,3 @@ export const filterUnreadMessagesInRange = (
     .filter(msg => msg.id >= fromId && msg.id <= toId);
   return filterUnreadMessageIds(messagesInRange.map(x => x.id), flags);
 };
-
-export const unreadToLimitedCount = (count: number): string =>
-  count < 100 ? count.toString() : '99+';