Fixed double camera overlay

[adrien-de-tocqueville]

Purpose of this PR

https://fogbugz.unity3d.com/f/cases/1361801/

needs a pretty recent trunk version to work

---

Testing status

tested the repro steps, tested it's still disabled after domain reload when entering play mode
tested switching pipelines

[github-actions]

Hi! This comment will help you figure out which jobs to run before merging your PR. The suggestions are dynamic based on what files you have changed.
Link to Yamato: https://yamato.cds.internal.unity3d.com/jobs/902-Graphics
Search for your PR branch using the sidebar on the left, then add the following segment(s) to the end of the URL (you may need multiple tabs depending on how many packages you change)

HDRP
/.yamato%252Fall-hdrp.yml%2523PR_HDRP_trunk
With changes to HDRP packages, you should also run
/.yamato%252Fall-lightmapper.yml%2523PR_LightMapper_trunk

Depending on the scope of your PR, you may need to run more jobs than what has been suggested. Please speak to your lead or a Graphics SDET (#devs-graphics-automation) if you are unsure.

[JMargevics]

The case is pretty simple, testing done is sufficient. Approving as is 👍✔

[sebastienlagarde]

Note for sed: This need a C++ PR for 21.2 for the backport