MobileNet: Update QNN EP example

[jambayk]

Describe your changes

MobileNet QNN EP example was outdated. QNN EP no longer requires x86 env for dev and arm env for inference. There is only one windows x86 package that can do both.

• Removed mobilenet_qnn_ep.py launcher script since a workflow json is enough.
• Added dynamic -> static shape step as a pass instead of during model download. This makes the static shape requirement clear to the user.
• Simplified data config.
• Download files uses command list instead of string to run subprocess. Otherwise, there are potential issues with paths being split incorrectly.

Checklist before requesting a review

• Add unit tests for this change.
• Make sure all tests can pass.
• Update documents if necessary.
• Lint and apply fixes to your code by running lintrunner -a
• Is this a user-facing change? If yes, give a description of this change to be included in the release notes.
• Is this PR including examples changes? If yes, please remember to update example documentation in a follow-up PR.

(Optional) Issue link