Remove CMD from wg-actuator dockerfile

[BrianJKoopman]

Description

See title.

Motivation and Context

The CMD was overriding the crossbar address configuration set by environment variables when trying to setup at the site.

How Has This Been Tested?

I built a test image at the site and ran it with this patch. It's working.

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 not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.