No STORAGE_PERMISSIONS to grant in new model.

When a developer has enabled the new Q storage model, the legacy
READ/WRITE_EXTERNAL_STORAGE permissions are no longer runtime
permissions, and we shouldn't try granting them any longer, since
they'd fail with a SecurityException.

Bug: 113039719
Test: manual
Change-Id: Idbb246378583832da12576dc17138142f1a6d2f5