How to reproduce:
1. Create a new "Universal Render Pipeline" project
2. In the Editor open Package Manager window
3. Make sure that "Show Dependencies" is enabled in the "Advanced" dropdown at the top of the Package Manager window near the search bar
4. In the package list on the left, select the "Universal RP" package
5. Observe the dependency list under the package description (open the "Dependencies" section if it's closed)

Expected result: The "Physics 2D" package is listed under "Dependencies"
Actual result: There is no "Physics 2D" package listed under "Dependencies"

Reproducible with: 2019.4.2f1 (7.3.1, 7.4.1), 2020.1.0b14, 2020.2.0a15 (8.1.0)
Could not test with: 2018.4.24f1 (4.10.0) (Package Manager doesn't show dependencies)

Note: Tested on Ubuntu 18.04 and Windows 10