Remove unused permissions on Android

[eirikurn]

We should not need these permissions. But we need to test on an actual device, just to be safe:

READ_EXTERNAL_STORAGE
WRITE_EXTERNAL_STORAGE
SYSTEM_ALERT_WINDOW
READ_INTERNAL_STORAGE

[Gunni]

@eirikurn if you can provide a build, i'm happy to test it

[Gunni]

Would it not also be sensible to remove READ_PHONE_STATE?

[eirikurn]

Hm. I assumed we'd need READ_PHONE_STATE if we'd want to automatically fill the phone number and verification code.

But it sounds like maybe we don't need this permission to implement this flow:

https://developers.google.com/identity/sms-retriever/overview

I'll remove these and send you a build for testing.