refactor(jni): unwrap useless unsafe blocks

[fu050409]

Hi there!

I'm glad to see someone trying to rewrite unidbg using Rust, it's a creation.

This is a simple commit, I just removed some unnecessary references and unsafe blocks.

I don't know if you mind if I make the following more work:

1. refactor the project structure to monorepo, i.e. migrate to crates, which is a common project structure used in the community, and I think this applies to rnidbg as well.
2. format the project code and even add a husky hook to make sure our code is compliant with the Rust programming paradigm.
3. enable clippy to do checks for the code to help us write more elegant code.
4. add continuous integration to the project for unit and integration testing, in fact not sure if it's my environment or not, I have an error in my main.rs.

Finally, thank you for your awesome work.

[fuqiuluo]

The test cases of this project extensively used the business of a company within China as an example. When submitting the source code, due to security and legal considerations, a large amount of these test codes were deleted.

But sincerely thank you for your submission.