Update migration guide to remove XhrHttpClient (Azure#20364)

* Update migration guide

* Spelling

sdk/test-utils/recorder/MIGRATION.md

@@ -15,7 +15,7 @@ The new recorder is version 2.0.0 of the `@azure-tools/test-recorder` package. U
   // ...
   "devDependencies": {
     // ...
-    "@azure-tools/test-credential" : "^1.0.0", // If you're using `@azure/identity` in your tests 
+    "@azure-tools/test-credential": "^1.0.0", // If you're using `@azure/identity` in your tests
     "@azure-tools/test-recorder": "^2.0.0"
   }
 }
@@ -122,6 +122,19 @@ await recorder.stop();
 
 It is important that `recorder.stop()` is called, or otherwise the next test will throw an error when trying to start the already started recorder. Additionally, it is important that both the `start` and `stop` calls are awaited, for similar reasons.
 
+## XHRHttpClient
+
+The legacy recorder didn't support recording browser calls made through the Fetch API. As a result, when fetch API was introduced in `core-rest-pipeline` a workaround was applied to the libraries not yet migrated to the new recorder, this workaround needs to be removed as part of the migration. Make the following changes, typically located in `utils/recordedClient.ts`
+
+```diff
+- const httpClient = isNode || isLiveMode() ? undefined : createXhrHttpClient();
+```
+
+```diff
+- recorder.configureClientOptions({ httpClient, ...options })
++ recorder.configureClientOptions(options)
+```
+
 ## Environment variables
 
 In the legacy recorder, the `replaceableVariables` option could be used to specify environment variables that would be replaced in the recording and set during playback. This could be used to ensure that secrets and user-specific options do not appear in the recording body.
@@ -283,7 +296,7 @@ const {
 
 // reporters - to be removed
       "json-to-file"
-      
+
 /* ... */
 // jsonToFileReporter - to be removed
 jsonToFileReporter: {
@@ -298,6 +311,7 @@ browserConsoleLogOptions: {
 ```
 
 Remove the following "devDependencies" from `package.json`
+
 ```js
    "karma-json-preprocessor": "^0.3.3",
    "karma-json-to-file-reporter": "^1.0.1",