Set default dtype

[JiangZhaoh]

Description

#17283 cause an issue #18193. So I depart dtype flag from npx.set_np()

Checklist

Essentials

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Changes

• Feature1, tests, (and when applicable, API doc)
• Feature2, tests, (and when applicable, API doc)

Comments

• If this change is a backward incompatible change, why must this change be made.
• Interesting edge cases to note here

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