Remove plugins with required inputs

[erezrokah]

Some plugins fail UI installation since the have required inputs:

 - netlify-plugin-brand-guardian
 - netlify-plugin-rss
 - netlify-plugin-add-instagram

We should remove them as they fail the build immediately when installed from UI.

This is only a partial list

[erezrokah]

Fixed via #58

[erezrokah]

Re-opening, we should also remove:

• https://github.com/philhawksworth/netlify-plugin-fetch-feeds
• https://github.com/daviddarnes/netlify-plugin-ghost-markdown

[ehmicky]

Should we send PRs to those plugins to add default values to those plugins?
Or post an issue asking the plugin author to add those?

[erezrokah]

I would say - if it's a small PR we can do it ourselves.
Not sure how a default value would look like for the ghost plugin

[erezrokah]

Also related https://github.com/getsentry/sentry-netlify-build-plugin, we just need to open a PR for them to remove the required inputs as they already fallback to env variables.

[verythorough]

@erezrokah Does the Ghost plugin not work when the required env vars are set?

[erezrokah]

The Ghost plugin has required inputs so it fails validation in Netlify build when installed from UI.
Even if they change the inputs to not required, they currently don't have fallback code like the sentry plugin.