Remove imports from expo

[raajnadar]

Remove imports from expo package

expo/expo#4501 to remove this warning.

react-native-paper/src/components/Appbar/AppbarHeader.js

Line 36 in 8746aba

global.__expo && global.__expo.Constants

react-native-paper/src/components/Icon.js

Line 13 in 8746aba

if (global.__expo && global.__expo.Icon && global.__expo.Icon.MaterialIcons) {

[brentvatne]

not necessary to remove these as we have patched the expo global to not raise these warnings in expo@33.0.4. in the future when optional imports are supported in metro we can get rid of the global and instead just wrap an import with try/catch to make it optional

[ferrannp]

Awesome!