Revert D47573238 - "[ET][Portable] Dtype compliance: clamp" (#77)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/77

D47573238 broke pytorch-edge-run-executorch-transcribe-bin

Original commit changeset: c083d810365e

Original Phabricator Diff: D47573238

Reviewed By: anticlockwise

Differential Revision: D48456015

fbshipit-source-id: 1975e574c3e229e5d4d32bc661a4104dd32dab00