migrate to expo-linear-gradient (#3420)

* replace packages

* rm useless alias from webpack config

* fix accidental double commit

* replace all usages

src/components/Button.tsx

@@ -11,7 +11,7 @@ import {
   View,
   ViewStyle,
 } from 'react-native'
-import LinearGradient from 'react-native-linear-gradient'
+import LinearGradient from 'expo-linear-gradient'
 import {Trans} from '@lingui/macro'
 
 import {android, atoms as a, flatten, tokens, useTheme} from '#/alf'

src/components/GradientFill.tsx

@@ -1,5 +1,5 @@
 import React from 'react'
-import LinearGradient from 'react-native-linear-gradient'
+import LinearGradient from 'expo-linear-gradient'
 
 import {atoms as a, tokens} from '#/alf'