As listed in our article How do we control who can access and use Design Tools? hiding the Design Tools launch button but leaving the Multi Tool and Upload/Embed Image Tool available is a popular option.
To do this, you will need to access your global JavaScript.
Change this line:
hideButton: false,
to
hideButton: true,
It is typically the 11th line down within the Design Tools portion of your JS.
This will hide the launch button but if a user knows one of the two keyboard shortcuts, they will still be able to access the Rich Content Editor Tools.