Update ReactElement.js

[Gregoirevda]

As far as I know, only React global has createElement property. So, if this check is made: https://github.com/facebook/react/blob/master/packages/react/src/React.js#L43 there shouldn't be any __DEV__ checks in the 'non validation' file?

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[jquense]

Hey there. So all validations are removed in the production copy via dead code elimination, so there is no worry about warnings slipping into the prod build. This change however, will remove those warnings for both dev and prod builds which is not what we want. Notice that ReactElementValidator imports ReactElement, so the warnings are added on top of what's already in ReactElement

[Gregoirevda]

Oh ok! It's not ReactElementValidator or ReactElement, but more ReactElementValidator that is an extension of ReactElement.