the button "Remove" should be deactivated when a marked shortcut can't be removed

[ralf3u]

in the Global-Actions-Manager-window:
the button "Remove" should be deactivated instead of activated when a marked shortcut can't be removed from the list

Expected Behavior

the button "Remove" should be deactivated when a marked shortcut can't be removed from the list

Current Behavior

the button "Remove" is still activated when a marked shortcut can't be removed from the list

Possible Solution

the button "Remove" should be deactivated when a marked shortcut can't be removed from the list

Steps to Reproduce (for bugs)

1. open the Global-Actions-Manager-window
2. mark a shortcut that can't be removed from the list, like for example "Show/hide main menu": the button "Remove" is still activated

Context

if the button "Remove" is still activated when a marked shortcut can't be removed from the list, and if then a user is pressing the "Remove"-button, but nothing happens, the user could think that there is a mistake in the software

System Information

• Distribution & Version: Lubuntu 20.10
• Qt Version: 0.15.0