Use new dataManagementLabel AIDL in Backup Settings

1) Uses new AIDL method getDataManagementLabelForUser
2) Changes data management label type from String to CharSequence

Bug: 113856654
Test: atest $(find \
packages/apps/Settings/tests/robotests/src/com/android/settings/backup \
-name '*Test.java')

Change-Id: I2325527c67878467b96fb93de50faafe153fdb21