Update memory plan default to use ConstraintBased instead of HintBased (#1399)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/1399

Hintbased uses whatever the inputs were while constraint based uses the constraints present in the program. Hint based doesnt seem to work for data dependent, and is a legacy pass before the constrain api was added.

There should only be one method to pass shape information about your program and that should be whatever export uses, executorch shouldnt have this concrete shape back door of hint based.

Reviewed By: tarun292

Differential Revision: D51905989

fbshipit-source-id: ba9b07e7427314f82d7ef2decd583404b10b7f5a