To reproduce:
1. Open attached project "ImageEffectscalls.zip"
2. Make sure that Allow HDR and Allow MSAA is disabled on the Main Camera
3. Open Frame Debugger window
4. Observe as there are no Camera.ImageEffects calls
5. Install Post Processing package from Package Manager window
6. Add Post Processing Layer component to the Main Camera
7. Uninstall Post Processing package
8. Remove the component from the Main Camera
9. Observe the Frame Renderer window again

Expected result: no Camera.ImageEffects calls
Actual result: there is one Camera.ImageEffects call with Hidden/BlitCopy subshader

Reproduced on:
2018.2.0b9 2018.2.20f1 2018.3.4f1

Post Processing version:
-2.1.3
-2.0.10
-2.0.5

-2.0.2 / 2.0.3 - no Post Processing components

Not reproduced on:
2019.1.0b2 2019.2.0a4

Notes:
-There is no Package Manager in 2017.4
-There are no Post Processing components to add to the Camera on 2018.2.0a1 - 2018.2.0a4
-On 2018.2.0a5 - 2018.2.0b8 Camera.ImageEffects is already present in frame debugger without Post Processing package.