Remove readonly for uploadtimestamp (#15765)

Co-authored-by: Dongwei Wang <[email protected]>

Author: idear1203

specification/synapse/resource-manager/Microsoft.Synapse/preview/2019-06-01-preview/bigDataPool.json

@@ -565,8 +565,7 @@
         "uploadedTimestamp": {
           "type": "string",
           "format": "date-time",
-          "description": "The last update time of the library.",
-          "readOnly": true
+          "description": "The last update time of the library."
         },
         "type": {
           "type": "string",

specification/synapse/resource-manager/Microsoft.Synapse/preview/2021-06-01-preview/bigDataPool.json

@@ -567,8 +567,7 @@
         "uploadedTimestamp": {
           "type": "string",
           "format": "date-time",
-          "description": "The last update time of the library.",
-          "readOnly": true
+          "description": "The last update time of the library."
         },
         "type": {
           "type": "string",