Reset vm_size and count to None under agent pool profile for VMAS migration (#8756)

* fix VMAS migration

* Update version

---------

Co-authored-by: [email protected] <reneeli>

Author: reneeli123

src/aks-preview/HISTORY.rst

@@ -12,6 +12,10 @@ To release a new version, please select a new version number (usually plus 1 to
 Pending
 +++++++
 
+17.0.0b4
+++++++++
+* Reset vm_size and count to None for `az aks update --migrate-vmas-to-vms`
+
 17.0.0b3
 ++++++++
 * Add default value of option `--vm-sizes` for `az aks create` and `az aks nodepool add`.

src/aks-preview/azext_aks_preview/managed_cluster_decorator.py

@@ -5368,6 +5368,9 @@ def update_vmas_to_vms(self, mc: ManagedCluster) -> ManagedCluster:
             if mc.network_profile.load_balancer_sku == CONST_LOAD_BALANCER_SKU_BASIC:
                 mc.network_profile.load_balancer_sku = CONST_LOAD_BALANCER_SKU_STANDARD
 
+            mc.agent_pool_profiles[0].count = None
+            mc.agent_pool_profiles[0].vm_size = None
+
         return mc
 
     def update_mc_profile_preview(self) -> ManagedCluster: