d/aws_memorydb_user(doc): fix copypasta

website/docs/d/memorydb_user.html.markdown

@@ -32,7 +32,7 @@ This data source exports the following attributes in addition to the arguments a
 * `access_string` - Access permissions string used for this user.
 * `arn` - ARN of the user.
 * `authentication_mode` - Denotes the user's authentication properties.
-    * `password_count` - (Optional) Number of passwords belonging to the user if `type` is set to `password`.
+    * `password_count` - Number of passwords belonging to the user if `type` is set to `password`.
     * `type` - Type of authentication configured.
 * `minimum_engine_version` - Minimum engine version supported for the user.
 * `tags` - Map of tags assigned to the user.