delete docs of removed plugins

[JanMa]

This deletes documentation for the plugins which are no longer officially supported by OpenBao according to the plugin proposal

[cipherboy]

I think the following additional docs need to go:

./content/docs/agent-and-proxy/autoauth/methods/{aws,alicloud}.mdx ## And more

I think there's also a few references here and there to removed stuff, e.g.:

content/api-docs/system/plugins-catalog.mdx:43:            "mssql-database-plugin",

(listing of plugins from an API response)

Hmm, this also doesn't build:

Please add these paths to the "../content/docs" nav data file, or remove the .mdx files. If you want the pages to exist but not be linked in the navigation, you can add a "hidden" property to the page object in the navigation structure.

[
  "commands/namespace"
]

(Edit: I guess this was an issue in #65)

But over all, this looks very good! Thanks @JanMa!

[JanMa]

Thanks @cipherboy , seems like the docs are littered with examples for the AWS secret engine and some others we removed. I'm in the process of cleaning that up

[cipherboy]

Looks very good, thanks @JanMa!