Re-enable storage permissions and remove unbranded-test flavour

[ngaruko]

This ticket in cht-android re-enable the storage permission that was removed last year, with a new flavour unbranded-test created.
I would suggest we remove it to avoid confusion in the future.
Also, think of re-enabling the storage permission for partners who use app launcher.

[latin-panda]

Cross posting here for the record:

• unbranded_test is removed.
• Partners will need to add the permission by themselves, so they can control when to release it and when communicate the change to their CHWs. A partner might want to add a permission if they are using a feature that requires it. Because of that, we won't update any of the partners' flavor.