Templates to create new projects from used to have Presets assets in them. Those presets have been deleted from the templates at some point but the PresetManager didn't get updated, it simply lost its reference. The PresetManager should be wiped in the templates so the Preset Manager isn't populated with missing references slots.

3D Template in 2018.3 (2019.1.0a3 is already cleaned)
- Create a new project using 3D template
- Open the Edit -> Settings panel and browse to the PresetManager window
Result: The preset manager is populated with three presets slots, all missing their references (Light, AudioImporter and TextureImporter)

2D Template
- Create another project using the 2D template this time
- Open the Edit -> Settings panel and browse to the PresetManager window
Result: The prset manager is populated with one Camera preset slot, missing its reference

We'll also need to make sure that the other templates are also updated correctly.

----------------------------------
NOTE
2019.1.0a3: 3D template has already been fixed, but still need an update for 2D
2018.3.0b5: All templates need to be updated to clear the preset manager.
----------------------------------