fix: remove style-src directive checks

[jasonbarry]

• We were getting a lot of Refused to apply a stylesheet because its hash, its nonce, or 'unsafe-inline' does not appear in the style-src directive of the Content Security Policy. messages in console when deployed to netlify-react-ui. We're unclear why, but a cursory search turned up this StackOverflow post. This PR goes back to only setting the nonce on the script-src directive.
• Adds in missing report-uri directive if a CSP is provided without one
• Simplifies short-circuit condition based on request and response headers

[netlify]

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