Fixed "p" prefix

Summary: The Android linter was enforcing the "p" prefix on all non-public classes. It's now only being enforced on nested classes like it should be.

Test Plan: View updated unit test cases.

Reviewers: mbishop, jstarke, mportune

Reviewed By: mbishop

Maniphest Tasks: T3591

Differential Revision: https://devportal.imobile3.com/D5859