fix(firestore, android): remove usage of Guava library

there was only one usage of Guava in firestore, and it was easily
replaced with a for loop which eliminates the dependency

this is important in the context of firebase-android-sdk where guava
is no longer transitively available - best to remove it here as well
vs bring it in directly as a dependency we specifically we need

packages/firestore/android/src/reactnative/java/io/invertase/firebase/firestore/ReactNativeFirebaseFirestoreSerialize.java

@@ -28,7 +28,6 @@
 import com.facebook.react.bridge.ReadableMapKeySetIterator;
 import com.facebook.react.bridge.WritableArray;
 import com.facebook.react.bridge.WritableMap;
-import com.google.common.collect.Iterables;
 import com.google.firebase.Timestamp;
 import com.google.firebase.firestore.Blob;
 import com.google.firebase.firestore.DocumentChange;
@@ -199,10 +198,12 @@ private static WritableArray documentChangesToWritableArray(
       boolean isMetadataChange = false;
       if (checkIfMetadataChange) {
         int hashCode = documentChange.hashCode();
-        DocumentChange exists =
-            Iterables.tryFind(
-                    comparableDocumentChanges, docChange -> docChange.hashCode() == hashCode)
-                .orNull();
+        DocumentChange exists = null;
+        for (DocumentChange docChange : comparableDocumentChanges) {
+          if (docChange.hashCode() == hashCode) {
+            exists = docChange;
+          }
+        }
 
         // Exists in docChanges with meta, but doesnt exist in docChanges without meta
         if (exists == null) {