Summary:
We need to remove adding png file extension when path has not extension. Two reasons:
1. `imageWithContentsOfFile` or other `UIKit` methods can load png image correctly, even if path has not `png` file extension.
2. Sometimes, people may have file that actually not have file extension, it's the designated behavior for user. Like #23844 .
CC. sahrens cpojer .
[iOS] [Fixed] - Remove explicitly add png file extension when load local image
Pull Request resolved: https://github.com/facebook/react-native/pull/23864
Reviewed By: shergin
Differential Revision: D14425373
Pulled By: hramos
fbshipit-source-id: 3cc06c9a3d68cadf652c1de742f3cce26258c874
e40a76715a