Remove nullary continuation form of then
Remove nullary continuation form of then

Summary:
Remove the form of Future::then that could take a continuation with no parameters, to force consistent use of parameters.

This form was already deprecated.

Reviewed By: Orvid

Differential Revision: D10219141

fbshipit-source-id: 4f8bdeaf617d8e78a5c85aa1374f6a0d38d63da9

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