The "Notification Area" cannot be removed

[David Hedlund]

#### Expected behaviour
Add a "Remove" button to the "Add to Panel":
See https://github.com/mate-desktop/mate-panel/issues/1398

#### Actual behaviour
I could not remove the "Notification Area"

#### Steps to reproduce the behaviour
To remove "Indicator Applet Complete" you first mouse right-click it and select uncheck "Lock To Panel" to it, and then you mouse right-click it again and select "Remove From Panel". However, for the"Notification Area", this is not possible:
* Right mouse-click on program icons in the "Notification Area" is reserved for program options (for example this is how you quit programs, you can try this with the package _workrave_).
* Left-mouse click will open the programs in the "Notification Area".

#### MATE general version
1.26.0

#### Package version
1.26.0

#### Linux Distribution
Ubuntu MATE 23.04