Remove unused function parameter (#344)

Author: gregfenton

firestore/test.solution-counters.js

@@ -22,7 +22,7 @@ function createCounter(ref, num_shards) {
 // [END create_counter]
 
 // [START increment_counter]
-function incrementCounter(db, ref, num_shards) {
+function incrementCounter(ref, num_shards) {
     // Select a shard of the counter at random
     const shard_id = Math.floor(Math.random() * num_shards).toString();
     const shard_ref = ref.collection('shards').doc(shard_id);
@@ -67,15 +67,15 @@ describe("firestore-solution-counters", () => {
             // Create a counter, then increment it
             const ref = db.collection('counters').doc();
             return createCounter(ref, 10).then(() => {
-                return incrementCounter(db, ref, 10);
+                return incrementCounter(ref, 10);
             });
         });
 
         it("should get the count of a counter", () => {
             // Create a counter, increment it, then get the count
             const ref = db.collection('counters').doc();
             return createCounter(ref, 10).then(() => {
-                return incrementCounter(db, ref, 10);
+                return incrementCounter(ref, 10);
             }).then(() => {
                 return getCount(ref);
             });