WSLA: Switch to using the system distro vhd.

[benhillis]

This changes moves WSLA to use the WSL system distro vhd instead of its own. This will allow for lower disk and memory usage for the product.

[Copilot]

Pull request overview

This PR transitions WSLA (Windows Subsystem for Linux Application) from using a separate, custom VHD file (wslarootfs.vhd) to using the shared WSL system distro VHD (system.vhd). This consolidation aims to reduce disk and memory usage across the WSL product.

Changes:

• Removed dependency on the Microsoft.WSL.WslaRootfs NuGet package
• Updated code to reference system.vhd instead of wslarootfs.vhd in the fallback path
• Changed the preprocessor macro from WSLA_TEST_DISTRO_PATH to WSL_SYSTEM_DISTRO_PATH for consistency
• Upgraded Microsoft.WSLg package from version 1.0.72 to 1.0.74

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/windows/wslaservice/exe/WSLASession.cpp	Updates WSLA session to use WSL_SYSTEM_DISTRO_PATH macro and system.vhd instead of WSLA_TEST_DISTRO_PATH and wslarootfs.vhd
packages.config	Removes Microsoft.WSL.WslaRootfs package dependency and upgrades Microsoft.WSLg to version 1.0.74
msipackage/package.wix.in	Removes the conditional packaging of wslarootfs.vhd file from the MSI installer
UserConfig.cmake.sample	Removes icacls permission command for the now-unused rootfs.vhd file
CMakeLists.txt	Removes WSLA_TEST_DISTRO NuGet package reference and WSLA_TEST_DISTRO_PATH compile definition