ThemePicker: Drop default permissions

This reverts commit b5642117.

Allowing storage permissions to the application violates
DefaultPermissionGrantPolicy.

Hence, drop the default permission and let user enable them on
first run in order to get wallpaper preview.

Issue: FP3-A13#35
Test: run gts -m GtsPermissionTestCases -t com.google.android.permission.gts.DefaultPermissionGrantPolicyTest
Change-Id: I7eefdf4330e32910447b1f3e82069ec30bec9a3f