[Identity] Remove outdated jobs from test pipeline (Azure#53297)

* Remove additional  jobs from tests.yml

* Remove platform-matrix.json configuration file

Author: JonathanCrd

sdk/identity/platform-matrix.json

@@ -5,11 +5,6 @@ extends:
   parameters:
     TimeoutInMinutes: 120
     PersistOidcToken: true
-    AdditionalMatrixConfigs:
-      - Name: identity_msi
-        Path: sdk/identity/platform-matrix.json
-        Selection: sparse
-        GenerateVMJobs: true
     ServiceDirectory: identity
     CloudConfig:
       Public: