Removed Engine Node from SUGCON package.json files

[robearlam]

Vercel have removed support for Node12, which has broken our builds. A better solution is to remove the engine definition from our package.json, allowing the engine to be defined within the Vercel dashboard itself. This PR makes that change.

Closes #408

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:

• I have read the Contributing guide.
• My code/comments/docs fully adhere to the Code of Conduct.
• My change is a code change.
• My change is a documentation change and there are NO other updates required.

[thomas-desmond]

approved