Revert accidental matrix config changes to identity ci pipeline (#16762)

Author: benbp

sdk/identity/ci.yml

@@ -29,11 +29,14 @@ extends:
   template: ../../eng/pipelines/templates/stages/archetype-sdk-client.yml
   parameters:
     ServiceDirectory: identity
-    AdditionalMatrixConfigs:
-      - Name: Identity_live_test
-        Path: sdk/identity/platform-matrix.json
-        Selection: sparse
-        GenerateVMJobs: true
+    AdditionalTestMatrix:
+      Linux_Python35_msal:
+        OSVmImage: 'ubuntu-18.04'
+        PythonVersion: '3.5'
+        CoverageArg: ''
+        RunForPR: false
+        InjectedPackages: 'git+https://github.com/AzureAD/microsoft-authentication-library-for-python@dev'
+
 
     Artifacts:
     - name: azure_identity