[WIP] Remove deprecated isNullOrUndefined function from DeleteLastServicePlanStep

[Copilot]

• Inspect current appservice implementation and test commands
• Run appservice lint/build/test to capture baseline status
• Replace deprecated isNullOrUndefined usage in DeleteLastServicePlanStep
• Bump appservice package minor version
• Run targeted validation (lint/build/test) after changes
• Run parallel validation and report final status

Original prompt

The appservice package uses the deprecated isNullOrUndefined function from Node's util module in one file:

1. appservice/src/deleteSite/DeleteLastServicePlanStep.ts — has import { isNullOrUndefined } from "util";

util.isNullOrUndefined has been deprecated since Node 4.0.0.

Changes needed:

1. Remove the import { isNullOrUndefined } from "util"; line from DeleteLastServicePlanStep.ts.
2. Replace all usages of isNullOrUndefined(x) with x === null || x === undefined (or x == null if that's cleaner in context).
3. Bump the minor version in appservice/package.json (e.g., if it's 1.2.3, bump to 1.3.0).
4. Ensure existing tests still pass.

Do NOT touch any files outside the appservice/ directory.

[bwateratmsft]

Actually going to close this to use the version from the utils package.