Add new line at the end of release note files (#6257)

Also, remove the unused `make_release_notes.py` file

Author: rlazo

buildSrc/src/main/java/com/google/firebase/gradle/plugins/MakeReleaseNotesTask.kt

@@ -134,7 +134,7 @@ abstract class MakeReleaseNotesTask : DefaultTask() {
         .trimMargin()
         .trim()
 
-    releaseNotesFile.asFile.get().writeText(releaseNotes)
+    releaseNotesFile.asFile.get().writeText(releaseNotes + "\n")
   }
 
   /**