migrate to expo-linear-gradient (#3420)

* replace packages

* rm useless alias from webpack config

* fix accidental double commit

* replace all usages

src/view/com/modals/DeleteAccount.tsx

@@ -6,7 +6,7 @@ import {
   TouchableOpacity,
   View,
 } from 'react-native'
-import LinearGradient from 'react-native-linear-gradient'
+import LinearGradient from 'expo-linear-gradient'
 import {msg, Trans} from '@lingui/macro'
 import {useLingui} from '@lingui/react'