Fix/rm content descriptor example

[meowsbits]

Following from conversation here: https://github.com/open-rpc/spec/issues/315#issuecomment-718259456

Edits are allowed by maintainers; feel free to push at will.

[BelfordZ]

:tada: This PR is included in version 1.3.0 :tada:

The release is available on:

• GitHub release
• 1.3.0

Your semantic-release bot :package::rocket: