Simplify FunctionRef

[swolchok]

Summary: Our version was so stripped down that it behaved equivalently to a function pointer.

Differential Revision: D56799169

[pytorch-bot[bot]]

:link: Helpful Links

:test_tube: See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/3442

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:white_check_mark: You can merge normally! (1 Unrelated Failure)

As of commit 40d142406c08fd445d94b38a96970ef00a05a4e6 with merge base 34aadcbb969a2e23c672b89a5fba19bc937eaf83 ():

FLAKY - The following job failed but was likely due to flakiness present on trunk:

• trunk / test-llama-runner-mac (fp32, cmake, portable) / macos-job (gh) File doesn't exist

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[digantdesai]

Our version was so stripped down that it behaved equivalently to a function pointer.

LOL thanks :)

Thanks @mergennachin for adding the trunk label - I guess this shouldn't break things since we are not introducing new features and should be c++11 compatible.

[swolchok]

this landed