Update language to comply with Android's inclusive language guidance

See https://source.android.com/setup/contribute/respectful-code for reference

Bug: 161896447
Test: refactoring CL, existing tests still pass. Verified by running
`atest UserBackupManagerServiceTest.java \
 utils/BackupEligibilityRulesTest.java`

Change-Id: Ibd97d99c64f6ddd82b3ba6e576f0a0ecd169d56f