Remove allow-screencapture check from Linux builds

[droidmonkey]

Overview

We check for the allow-screencapture command line flag on Linux even though it isn't defined as a flag. This throws a warning in the console.

Steps to Reproduce

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Expected Behavior

Actual Behavior

Context

KeePassXC - VERSION
Revision: REVISION

Operating System: Windows/Linux/macOS
Desktop Env: Gnome/KDE/XFCE/Mate/Cinnamon
Windowing System: X11/Wayland

[Organic-Marble]

I assume this refers to the message "QCommandLineParser: option not defined: "allow-screencapture"" I'm getting in the terminal after today's update. Also, the screenshot option in the View menu mentioned here https://9to5linux.com/keepassxc-2-7-5-password-manager-adds-new-option-to-allow-screenshots-botan-3-support is not present.