(Note: This will work based on your current theme)
Here is the Code Just go to AdminCP>Theme(Choose that theme which you have choosed for AdminCP)>Edit HTML & CSS> In CSS Tab> Find Custom.css and type the code below the generated code.
Code:
.cDashboard_bulletin {
display: none;
}
Demo of reCAPTCHA Notice
https://imgur.com/77ejAoZ