Revert "PhoneAccountRegistrarTest: use registrar as SYSTEM user"

This reverts commit 325aed4a731c875d9348972a869b2afcbc8a77ca.

Reason for revert: https://buganizer.corp.google.com/issues/383423749#comment7

Change-Id: I2e9d5422f941b90e01036ba570c7c3c6f5f4a472
1 file changed