Remove Invoke-RemoteScriptAsync (dead code)

[michaellwest]

Summary

Invoke-RemoteScriptAsync in modules/SPE/Invoke-RemoteScript.ps1 is exported from the module but effectively dead code:

• No callers anywhere in the codebase
• Tests are commented out in tests/integration/Remoting.Automation.Tests.ps1
• No documentation references it
• Returns raw Task objects requiring .Result access — awkward PowerShell UX

The -AsJob switch on Invoke-RemoteScript covers the same async use case and is actively used/documented.

Changes

• Remove Invoke-RemoteScriptAsync function from modules/SPE/Invoke-RemoteScript.ps1
• Remove from FunctionsToExport in modules/SPE/SPE.psd1
• Remove commented-out async tests from tests/integration/Remoting.Automation.Tests.ps1
• Remove supporting utilities if no longer needed: New-RunspacedDelegate.ps1, Invoke-GenericMethod.ps1

Justification

Cleaning up dead code as part of the 9.0 release. Major version bump makes this a non-breaking change window.