Still signing in with Account Activity UI in a few places

### Description

We have migrated signing the user into the app to use our `OnboardingFlowComposable`, but there are still a few places in the app where we're using `AccountActivity`. In addition to not providing the full onboarding flow, the AccountActivity does not allow the user to sign in with Google. We should remove any remaining places where the user is prompted to sign in with the AccountActivity.

### Step-by-step reproduction instructions

1. Tap on the EOY upgrade banner
2. Observe that the sign in screen does not offer the option of signing in with Google.

### Screenshots or screen recording

_No response_

### Did you search for existing bug reports?

- [X] I have searched for existing bug reports.

### Device, Operating system, and Pocket Casts app version

Samsung A13, Pocket Casts 7.50 development build, Android 13.

Start by tracing the EOY upgrade banner flow and searching for remaining sign-in prompts that use AccountActivity instead of OnboardingFlowComposable. Reproduce on the reported Android 13 setup, then verify every affected entry point presents the full onboarding flow, including Google sign-in.

Written by the indexing model from the issue text.