refactor: use TakePictureRequestEvent instead of PictureTakenEvent

This is better for a number of reasons, specially for code simplicity

mastodon/src/main/java/org/joinmastodon/android/events/PictureTakenEvent.java

@@ -1,13 +0,0 @@
-package org.joinmastodon.android.events;
-
-import android.net.Uri;
-
-import org.joinmastodon.android.model.Poll;
-
-public class PictureTakenEvent {
-    public Uri uri;
-
-    public PictureTakenEvent(Uri uri){
-        this.uri = uri;
-    }
-}

mastodon/src/main/java/org/joinmastodon/android/events/TakePictureRequestEvent.java

@@ -0,0 +1,6 @@
+package org.joinmastodon.android.events;
+
+public class TakePictureRequestEvent {
+    public TakePictureRequestEvent(){
+    }
+}