API Review: Make dataManagementLabel a CharSequence

Make the data management label a CharSequence for the system APIs:
- BackupManager#updateTransportAttributes
- BackupManager#getDataManagementLabel
- BackupTransport#dataManagementLabel

Renames dataManagementLabel -> dataManagementIntentLabel to change
return type

Removes getDataManagementLabel AIDL method as usages converted to use
"forUser" version in topic CL.

Bug: 113856654
Test: 1) atest RunBackupFrameworksServicesRoboTests
2) atest BackupManagerTransportAttributesHostSideTest
3) atest $(find \
frameworks/base/services/tests/servicestests/src/com/android/server/backup \
-name '*Test.java')
4) Manual: boot and verify transports registered properly using old API;
Modify LocalTransport to use new API, verify success

Change-Id: Ia48017156debe0a29684909f58927fa1fbf972f9