delete defaultProps from imported SVGs

[interim17]

Problem

Advances #381

Solution

This is a bit of a hack, just typecasting and deleting the defaultProps that seem to be added by gatsby-plugin-react-svg

Likely the better long-term fix is to move away from that plugin:
jacobmischka/gatsby-plugin-react-svg#59

My first few attempts to switch plugins were met with build issues. If we want a quick solution, I think this will remove the browser warnings, and we can look at switching plugins going forward?

[interim17]

@meganrm if you want to prioritize speed over beauty we can take this approach as a stop gap?