(DOCSP-42573) Update transactions in Functions info about read/write settings (#860)

Removing any mentions + code of creating a configuration object that
sets user's preferred read/write settings and passing it to the session
method. These settings are not configured in this context and not
respected.

## Pull Request Info

Jira ticket: https://jira.mongodb.org/browse/DOCSP-42573

### Staging Links
<!-- start insert-links -->
</li><li><a
href=https://deploy-preview-860--app-services.netlify.app/functions/mongodb/write>functions/mongodb/write</a></li>
<!-- end insert-links -->

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### Release Notes

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- **Define Data Access Permissions**
- Data Access Role Examples: Update CRUD Permissions example screenshots
and
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-->

### Review Guidelines


[REVIEWING.md](https://github.com/mongodb/docs-app-services/blob/master/REVIEWING.md)

Author: amalhotra-mdb

source/functions/mongodb/api/snippets/transactions.js

@@ -1,10 +1,10 @@
 exports = function () {
   const client = context.services.get("mongodb-atlas");
 
-  db = client.db("exampleDatabase");
+  const db = client.db("exampleDatabase");
 
-  accounts = db.collection("accounts");
-  browniePointsTrades = db.collection("browniePointsTrades");
+  const accounts = db.collection("accounts");
+  const browniePointsTrades = db.collection("browniePointsTrades");
 
   // create user accounts with initial balances
   accounts.insertOne({ name: "henry", browniePoints: 42 });
@@ -34,18 +34,11 @@ async function tradeBrowniePoints(
   // Step 1: Start a Client Session
   const session = client.startSession();
 
-  // Step 2: Optional. Define options to use for the transaction
-  const transactionOptions = {
-    readPreference: "primary",
-    readConcern: { level: "local" },
-    writeConcern: { w: "majority" },
-  };
-
-  // Step 3: Use withTransaction to start a transaction, execute the callback, and commit (or abort on error)
+  // Step 2: Use withTransaction to start a transaction, execute the callback, and commit (or abort on error)
   // Note: The callback for withTransaction MUST be async and/or return a Promise.
   try {
     await session.withTransaction(async () => {
-      // Step 4: Execute the queries you would like to include in one atomic transaction
+      // Step 3: Execute the queries you would like to include in one atomic transaction
       // Important:: You must pass the session to the operations
       await accounts.updateOne(
         { name: userSubtractPoints },
@@ -65,12 +58,12 @@ async function tradeBrowniePoints(
         },
         { session }
       );
-    }, transactionOptions);
+    });
   } catch (err) {
-    // Step 5: Handle errors with a transaction abort
+    // Step 4: Handle errors with a transaction abort
     await session.abortTransaction();
   } finally {
-    // Step 6: End the session when you complete the transaction
+    // Step 5: End the session when you complete the transaction
     await session.endSession();
   }
 }

source/functions/mongodb/write.txt

@@ -383,20 +383,12 @@ To perform a transaction:
 1. Obtain and start a client session with ``client.startSession()``.
 
 #. Call ``session.withTransaction()`` to define the transaction. The
-   method takes an async callback function and, optionally, a
-   configuration object that defines custom :manual:`read and write
-   settings
-   </core/transactions/#read-concern-write-concern-read-preference>` for
-   the transaction.
+   method takes an async callback function.
 
    .. code-block:: javascript
 
       session.withTransaction(async () => {
          // ... Run MongoDB operations in this callback
-      }, {
-          readPreference: "primary",
-          readConcern: { level: "local" },
-          writeConcern: { w: "majority" },
       })
 
 #. In the transaction callback function, run the MongoDB queries that
@@ -439,7 +431,7 @@ To perform a transaction:
       }
 
 The following example creates two users, "henry" and "michelle", and
-a uses a transaction to move "browniePoints" between those users
+uses a transaction to move "browniePoints" between those users
 atomically:
 
 .. literalinclude:: /functions/mongodb/api/snippets/transactions.js