Revert resizeMode to Stretch as unset (#53144)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/53144

Changelog: [Internal]
This is a fix to "unset" prop value for Image.
In my previous diff D79600137 I have changed this behaviour to have Cover as a default, but it is not "default" value, but rather "unset" value.

Reviewed By: rshest

Differential Revision: D79813759

fbshipit-source-id: cc6d43742e51fb2087d6023bd0ff50a3d54eed49