Bundles from previous builds end up in the out-dir even if removed from code

**Problem**

When specifying `--out-dir` on `dx bundle`, after all things are precompressed and renamed, it just copies the content of the /`target/dx/release/.../web/public/` folder, without any kind of check if that folder contains weird artifacts from previous builds

**Steps To Reproduce**

Steps to reproduce the behavior:

- Put in assets that you want in the code
- bundle the app with --out-dir
- remove said assets from the code
- bundle again, the out dir contains the removed assets

The removed assets will be found in the out-dir

**Expected behavior**

the out-dir should contain the correctly tree-shaked values from how assets are handled, and not contain junk from previous builds

Or just some good documentation explaining how to fix this

**Environment:**

- Dioxus version: 0.7
- OS info: Linux, x64_32
- App platform: web