do not overwrite PSModulePath when setting up build environment

[mwrock]

The PSModulePath environment variable is where Powershell looks for modules. When entering a powershell shell, powershell will ensure that its own modules directory which include the built in modules that ship with powershell are added to this variable when the shell starts.

If a plan includes something like:

function Invoke-SetupEnvironment {
    Push-RuntimeEnv "PSModulePath" "\hab\pkgs\$pkg_origin\$pkg_name\$pkg_version\$pkg_release\Modules"
}

This will overwrite the existing PSModulePath and potentially cause powershell commands that leverage the distribution bundled modules to fail.

An example would be any plan that takes a dep on core/dsc-core which includes the above code.

This PR does 3 things:

1. Sets the PSModulePath in the Studio creation code so that any module paths other than those included with the powershell vendored in the studio are not included.
2. Add PSModulePath to the list of variables in hab-plan-build that should not be overwritten.
3. Removes a function I found to be entirely dead code.

Signed-off-by: mwrock matt@mattwrock.com

[christophermaier]

Is it significant that this "Runtime", while above we have "RunTime" (note capitalization)?

(same with "Buildtime" below)

[mwrock]

No. Powershell hash keys and variables are not case sensitive.

[christophermaier]

Hrmm... maybe it'd be better to be consistent.

If nothing else, it'd stop me from asking these questions 😉