Rename PACKAGE_ROLLBACK_EXECUTED to ROLLBACK_COMMITTED.

Because there's no need to distinguish between package and other kinds
of rollbacks, and for rollback of staged installs, committed is a more
appropriate name than executed.

Bug: 112431924
Test: atest RollbackTest
Change-Id: I2a409de29ba82a7a3df2fd0b17f939795caa61d5