fix(e2e): drop hardcoded D2s_v3 system pool from MA35D scenarios

[ganeshkumarashok]

Summary

• Remove K8sSystemPoolSKU: \"Standard_D2s_v3\" from Test_AzureLinuxV3_MA35D and Test_AzureLinuxV3_MA35D_Scriptless
• Falls back to config.DefaultVMSKU (Standard_D2ds_v5) — same SKU every other scenario uses for the AKS system node pool
• The GPU SKU under test (Standard_NM16ads_MA35D) is unchanged

Background

Both MA35D scenarios pin Location: \"eastus\" (the only region with MA35D capacity) and override the system node pool to the older v3 SKU. The override predates the v5 default and is no longer necessary.

The pinned SKU is currently subscription-restricted across all eastus availability zones for the AB e2e subscription (8ecadfc9-...), so AKS cluster creation 400s before the GPU node under test can even be provisioned. Observed in PR #8228 GPU E2E build 161380177:

RESPONSE 400: 400 Bad Request
ERROR CODE: BadRequest
{
  \"code\": \"BadRequest\",
  \"message\": \"The VM size of 'Standard_D2s_v3' is currently not available in your subscription in location 'eastus'. All availability zones are restricted for this SKU. Please try another VM size or deploy to a different location.\"
}

This caused 5 reported failures in that run (the parent + leaf subtests for both MA35D scenarios), which had nothing to do with the PR being tested.

Why this fix

• Standard_D2ds_v5 is the established default for all e2e system pools (config/config.go: DefaultVMSKU)
• If D2ds_v5 were also restricted in eastus we'd see it across many GPU scenarios, not just MA35D — i.e. failure mode would be loud and broad, not silently misattributed to MA35D
• Smallest possible diff (2 lines per test)

Test plan

• Agentbaker GPU E2E (the only pipeline that exercises MA35D)
• Confirm cluster abe2e-kubenet-v4-* in eastus comes up cleanly with v5 system pool
• Confirm Test_AzureLinuxV3_MA35D and _Scriptless reach the GPU validators

[Copilot]

Pull request overview

Removes a hardcoded Kubernetes system node pool VM SKU from the two AzureLinuxV3 MA35D GPU e2e scenarios so they rely on the standard e2e default (config.Config.DefaultVMSKU), avoiding Standard_D2s_v3 availability/subscription restrictions in eastus while keeping the MA35D GPU SKU under test unchanged.

Changes:

• Dropped K8sSystemPoolSKU: "Standard_D2s_v3" from Test_AzureLinuxV3_MA35D.
• Dropped K8sSystemPoolSKU: "Standard_D2s_v3" from Test_AzureLinuxV3_MA35D_Scriptless.
• Left Location: "eastus" in place for MA35D capacity, allowing system pool SKU to fall back to config.Config.DefaultVMSKU.