Remove a @nullable annotation and an unnecessary dependency

Author: lfkellogg

firebase-appdistribution/src/main/java/com/google/firebase/appdistribution/impl/FeedbackSender.java

@@ -15,7 +15,6 @@
 package com.google.firebase.appdistribution.impl;
 
 import android.graphics.Bitmap;
-import androidx.annotation.NonNull;
 import com.google.android.gms.tasks.Task;
 import com.google.firebase.FirebaseApp;
 
@@ -28,7 +27,7 @@ class FeedbackSender {
     this.testerApiClient = testerApiClient;
   }
 
-  @NonNull
+  /** Get an instance of FeedbackSender. */
   static FeedbackSender getInstance() {
     return FirebaseApp.getInstance().get(FeedbackSender.class);
   }

firebase-appdistribution/src/main/java/com/google/firebase/appdistribution/impl/FirebaseAppDistributionRegistrar.java

@@ -46,7 +46,6 @@ public class FirebaseAppDistributionRegistrar implements ComponentRegistrar {
         Component.builder(FirebaseAppDistribution.class)
             .add(Dependency.required(FirebaseApp.class))
             .add(Dependency.requiredProvider(FirebaseInstallationsApi.class))
-            .add(Dependency.required(FeedbackSender.class))
             .factory(this::buildFirebaseAppDistribution)
             // construct FirebaseAppDistribution instance on startup so we can register for
             // activity lifecycle callbacks before the API is called