[Synapse] - change DatasetCompression type back to string (Azure#16076)

Co-authored-by: Dongwei Wang <dongwwa@microsoft.com>

Author: 2 people

specification/synapse/data-plane/Microsoft.Synapse/preview/2021-06-01-preview/entityTypes/Dataset.json

@@ -402,8 +402,8 @@
       "type": "object",
       "properties": {
         "type": {
-          "type": "object",
-          "description": "Type of dataset compression. Type: string (or Expression with resultType string)."
+          "type": "string",
+          "description": "Type of dataset compression."
         }
       },
       "additionalProperties": {

specification/synapse/data-plane/Microsoft.Synapse/stable/2020-12-01/entityTypes/Dataset.json

@@ -402,8 +402,8 @@
       "type": "object",
       "properties": {
         "type": {
-          "type": "object",
-          "description": "Type of dataset compression. Type: string (or Expression with resultType string)."
+          "type": "string",
+          "description": "Type of dataset compression."
         }
       },
       "additionalProperties": {