removed unnecesary let, changed to const

Author: aditi-khare-mongoDB

src/cmap/handshake/client_metadata.ts

@@ -92,7 +92,7 @@ type MakeClientMetadataOptions = Pick<MongoOptions, 'appName' | 'driverInfo'>;
  * 4. Truncate `platform`. -- special we do not truncate this field
  */
 export function makeClientMetadata(options: MakeClientMetadataOptions): ClientMetadata {
-  let metadataDocument = new LimitedSizeDocument(512);
+  const metadataDocument = new LimitedSizeDocument(512);
 
   const { appName = '' } = options;
   // Add app name first, it must be sent