Added delete poll route in backend

backend/src/repositories/poll.repo.js

@@ -28,4 +28,14 @@ export async function findPollsByCreatorId(id) {
     catch(err){
         throw err;
     }
+}
+
+export async function deletePollById(id) {
+    try {
+        const poll = await PollModel.findByIdAndDelete(id);
+        return poll;
+    }
+    catch(err){
+        throw err;
+    }
 }