How to reproduce:
1. Create "3D - High definition" project
2. Add point light \ dummy object
3. Create simple Flare
4. Attach flare to Point light flare field \ Lens Flare component
5. Enter Play Mode

Actual result: Lens Flare not working in HDRP preset project (Does not appear in Play mode)
Expected result: Lens flares are drawn normally (as in 2017 stable release)

Reproduced with: 2018.1.0b9, 2018.2.0a2

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Won't Fix:

SRP don't support the Overlay layer and Lens flare are render in Overlay.
Mean SRP doesn't support Lens Flare. This is an old feature that we want to deprecate anyway.
Note: This is general to SRP, either LW or HD (this bug is not specific HD).

Currently, the true issue is that SRP haven't disable fully the Overlay rendering pass, it is done after the Render() SRP and only in SceneView. This is what we will fix.