Default logo.svg and favicon.ico are copied to the build directory even if changed in global.json

**Operation System**: Windows

**DocFX Version Used**: 2.48.0.0

**Template used**: `statictoc`

**Steps to Reproduce**:

1. Create a DocFX project.
2. Override `_appLogoPath` and `_appFaviconPath` in `global.json` (e.g. as `images/logo.png` and `images/favicon.png`, respectively).
3. Build the project.

**Expected Behavior**: DocFX shouldn't copy its default `logo.svg` and `favicon.ico` files to `build` if they've been overridden in `global.json`.

**Actual Behavior**: It does.