Rename HSUM boot strategy const

Rename the const so that a future new const can share the same prefix BOOT_STRATEGY_.

Bug: 424267322
Flag: EXEMPT mechanical change
Test: atest FrameworksMockingServicesTests:com.android.server.pm.UserManagerServiceMockedTest
Change-Id: Iec095d7d97110f0495a8ea3f059f9801984c4177