The current version of `avidemux` (v2.7.0) breaks on master (see
https://hydra.nixos.org/build/75993794), the 18.03 build remains fine
(https://hydra.nixos.org/build/75935027).
The following changes have been applied:
* `glibc` compat patch is obsolete as it landed in upstream.
* Fixed QT_PLUGIN_PATH for QT binaries to avoid errors because of
missing plugins like this:
```
qt.qpa.plugin: Could not find the Qt platform plugin "xcb" in ""
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.
[1] 20081 abort /nix/store/rjwxc6ih15zwvvy71ss8bvnh56ibfbmj-avidemux-2.7.1/bin/avidemux3_qt5
```
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