Image file note remove when rendering pdf with output-dir option

Bug description

If you have some image file in your quarto and you want render a pdf using output-dir option, the image file are copied in the specified output directory and won't be removed after the rendering process.

Steps to reproduce

the _quarto.yml file

project: 
  output-dir: output

the index.qmd file

---
format:
  pdf
---

![my img](my_img.png)

put any image file in my_img.png

Expected behavior

only index.pdf is produced in the output directory

Actual behavior

index.pdf is produced in the output directory but my_img.png is also find in the output directory

Your environment

Ubuntu 24.04
Quarto 16.04
VSCodium 1.92.2

Quarto check output

quarto check
Quarto 1.6.40
[✓] Checking environment information...
      Quarto cache location: /home/lbeaulaton/.cache/quarto
[✓] Checking versions of quarto binary dependencies...
      Pandoc version 3.4.0: OK
      Dart Sass version 1.70.0: OK
      Deno version 1.46.3: OK
      Typst version 0.11.0: OK
[✓] Checking versions of quarto dependencies......OK
[✓] Checking Quarto installation......OK
      Version: 1.6.40
      Path: /opt/quarto/bin

[✓] Checking tools....................OK
      TinyTeX: (not installed)
      Chromium: (not installed)

[✓] Checking LaTeX....................OK
      Using: Installation From Path
      Path: /usr/bin
      Version: 2023

[✓] Checking basic markdown render....OK

[✓] Checking Python 3 installation....OK
      Version: 3.12.3
      Path: /usr/bin/python3
      Jupyter: 5.3.2
      Kernels: python3

(\) Checking Jupyter engine render....Traceback (most recent call last):
  File "/opt/quarto/share/jupyter/jupyter.py", line 21, in <module>
    from notebook import notebook_execute, RestartKernel
  File "/opt/quarto/share/jupyter/notebook.py", line 20, in <module>
    from nbclient import NotebookClient
ModuleNotFoundError: No module named 'nbclient'
[✓] Checking Jupyter engine render....OK

Reproduce the issue with the shown _quarto.yml and index.qmd files, using a local image and the output-dir option. Start by tracing how PDF rendering handles copied assets in the output directory. Done means rendering produces index.pdf in output without leaving my_img.png there.