Get rid of explicit SPICE unloading

[Mark2000]

Description

Merge one BSK is updated on pypi with spice PR: AVSLab/basilisk#1180

Uses new BSK spice behavior to limit overheads.

Type of change

• 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 not work as expected)

How should this pull request be reviewed?

• By commit
• All changes at once

How Has This Been Tested?

Tested in BSK PR.

Checklist

• I have performed a self-review of my code
• I have commented my code in hard-to-understand areas
• I have made corresponding changes to the documentation and release notes
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works