System UserInfo flags are set in UserTypeFactory

The System's default UserInfo flags are set in two possible places. We
move the "user-type" flags to UserTypeFactory, consistent with other
user types. This is just aesthetics. There is no functional change here.

We also mark FLAG_PRIMARY and isPrimary as deprecated. They are merely
synonymous with FLAG_SYSTEM and userId == 0.

Bug: 267536424
Test: Flash HSUM and non-HSUM builds and ensure system has correct flags
Change-Id: I759409d907120043f20b2341655a65cb372a0d21
Merged-In: I759409d907120043f20b2341655a65cb372a0d21