Move billing code to shared module.

app/src/main/java/org/thoughtcrime/securesms/billing/GooglePlayBillingApi.kt

@@ -1,30 +0,0 @@
-/*
- * Copyright 2024 Signal Messenger, LLC
- * SPDX-License-Identifier: AGPL-3.0-only
- */
-
-package org.thoughtcrime.securesms.billing
-
-import android.app.Activity
-
-/**
- * Variant interface for the BillingApi.
- */
-interface GooglePlayBillingApi {
-  fun isApiAvailable(): Boolean = false
-  suspend fun queryProducts() = Unit
-
-  /**
-   * Queries the user's current purchases. This enqueues a check and will
-   * propagate it to the normal callbacks in the api.
-   */
-  suspend fun queryPurchases() = Unit
-
-  suspend fun launchBillingFlow(activity: Activity) = Unit
-
-  /**
-   * Empty implementation, to be used when play services are available but
-   * GooglePlayBillingApi is not available.
-   */
-  object Empty : GooglePlayBillingApi
-}