Access Plan "Description" misbehaves when a "Classic" block exists on a course or membership

### 1. Reproduction Steps

+ Create a course
+ Add a "Classic Editor" block to it
+ Create an access plan
+ Save the course / access plan

### 2. Expected Behavior

+ Everything should be fine

### 3. Actual Behavior

+ The content from the Classic Block is pushed into the TinyMCE editor on the access plan

