fix: Remove init from AppChecker (#96)

* feat: Add functionality for the FirebaseAppCheck call

* fix: Remove unused import

* fix: Remove init from AppChecker

- amended AppChecker to allow for inistaniating Firebase within
init block within implementation of the interface

* refactor: Amend AppChecker to be fun inetrface

app/src/main/java/uk/gov/android/authentication/integrity/appcheck/AppChecker.kt

@@ -1,10 +1,7 @@
 package uk.gov.android.authentication.integrity.appcheck
 
-import android.content.Context
 import uk.gov.android.authentication.integrity.model.AppCheckToken
 
-interface AppChecker {
-    fun init(context: Context)
-
+fun interface AppChecker {
     suspend fun getAppCheckToken(): Result<AppCheckToken>
 }