clarify fidesops meta docs (#184)

docs/fidesops/docs/guides/datasets.md

@@ -106,7 +106,7 @@ dataset:
 	- `identity`: Signifies that this field is an identity value that can be used as the root for a traversal [See graph traversal](query_execution.md)
 	- `direction`(_Optional_): Accepted values are `from` or `to`. This determines how Fidesops uses the relationships to discover data. If the direction is `to`, Fidesops will only use data in the _source_ collection to discover data in the _referenced_ collection. If the direction is `from`, Fidesops will only use data in the _referenced_ collection to discover data in the _source_ collection. If the direction is omitted, Fidesops will traverse the relation in whatever direction works to discover all related data.
 	- `primary_key` (_Optional_): A boolean value that means that Fidesops will treat this field as a unique row identifier for generating update statements. If multiple fields are marked as primary keys the combination of their values will be treated as a combined key. In SQL terms, we'd issue a query that looked like `SELECT ... FROM TABLE WHERE primary_key_name_1 = value1 AND primary_key_name_2 = value2`. If no primary key is specified for any field on a collection, no updates will be generated against that collection.
-	- `data_type` (_Optional_): An indication of type of data held by this field. Data types are used to convert values to the appropriate type when those values are used in queries. Data types are also used to generate the appropriate masked value when running erasures, since Fidesops needs to know the type of data expected by the field in order to generate an appropriate masked value. Available datatypes are `string`, `integer`, `float`, `boolean`, `object_id`. `object` types are also supported for MongoDB.
+	- `data_type` (_Optional - Required only when processing erasure requests for masking strategies other than Null rewrite_): An indication of type of data held by this field. Data types are used to convert values to the appropriate type when those values are used in queries. Data types are also used to generate the appropriate masked value when running erasures, since Fidesops needs to know the type of data expected by the field in order to generate an appropriate masked value. Available datatypes are `string`, `integer`, `float`, `boolean`, `object_id`. `object` types are also supported for MongoDB.
 	- `length` (_Optional_): An indicator of field length.
 
 #### Object fields

docs/fidesops/docs/tutorial/annotate_datasets.md

@@ -48,15 +48,6 @@ the user by `email`, and from there, travel through other tables linked to `user
     identity: email
 ```
 
-Optional `fidesops_meta` fields:
-- `data_type`: only required for processing erasure requests, however, whenever specified, Fidesops will attempt to coerce the field's value to the type. For erasure requests in particular, Fidesops requires `data_type` to ensure that the configured masking strategy can process the value. Supported data types:
-  - `string`
-  - `integer`
-  - `float`
-  - `boolean`
-  - `object_id`
-- `length`: if `length` is specified, in an erasure request, Fidesops will truncate the end of the masked value to the specified `length`. This should be used if your database column has a length restriction. E.g. if a specific row has `email` of `jerry@mail.com`, and the masked value is `23982r3n8rupq8ewurnw`, and `length` is set to `10`, then the resulting update query will use the value `23982r3n8r`.
-
 ## Upload this Dataset to Fidesops
 
 For more detailed information, [see the Datasets Guide](../guides/datasets.md).