In drupal textarea field, it was always a pain to see the two links:
Text format showing list of available format, even if user is allowed to use one format only
And a link of About Text formats
Drupal 8 provided an easy but hidden way to hide this.
Do following steps:
Goto your content type
Click on Manage Form Display
For example, body is the field
Click on settings icon button on right hand side of body field
A small form will open up
Check on option - Hide the help link About text formats
Check on option - Hide text format guidelines
Save the content type
Clear cache and open the form
See the final form
Note: You did hide the two unwanted options in the form. But, you can still see the drop down of formats. This should be fine for most of the users. But, I did not want this. I did not want to confuse my users.