Retire deep copy of edge_program in to_backend method

[haowhsu-quic]

Qualcomm lowering flow is no longer requiring deep copy if #4297 merged. Could consider removing this.

[pytorch-bot]

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✅ You can merge normally! (2 Unrelated Failures)

As of commit e30ab88 with merge base 4a88318 ():

FLAKY - The following jobs failed but were likely due to flakiness present on trunk:

• Lint / Build failed (gh) (detected as infra flaky with no runner)
• pull / Build failed (gh) (detected as infra flaky with no runner)

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[cccclai]

Looks like there are some internal failure we'd need to fix..

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