Remove VM instructions from install_pecan

[dlebauer]

Description

This PR removes references to the VM from PEcAn documentation.

Motivation and Context

Since getting Docker up and running, we retired the VM and the latest available is v1.7.2

Review Time Estimate

• Immediately
• Within one week
• When possible

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My change requires a change to the documentation.
• My name is in the list of CITATION.cff
• I agree that PEcAn Project may distribute my contribution under any or all of
  • the same license as the existing code,
  • and/or the BSD 3-clause license.
• I have updated the CHANGELOG.md.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[robkooper]

Is there other info in the other docs?

[dlebauer]

@robkooper just removed everything explicitly referencing the PEcAn VM; left references to VMs as a way of explaining Docker (though yeah, maybe these are outdated now that Docker is more familiar) and as synonyms for server, e.g. in AWS cloud.