Remove dead code

Currently, plasma-desktop fails to build with the following error message:

/data/projects/src/plasma-desktop/kcms/keys/globalaccelmodel.cpp:184:83: error: no viable conversion from 'QList' to 'const QList' auto reply = m_globalAccelInterface->setForeignShortcut(actionId, keys);

given that Plasma requires KF 5.90 or newer, the ifdef can be removed.

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Edit: it fails to build because I was bisecting kglobalaccel a few days ago and so I have two kglobalaccel_version.h header files in my usr/include

./KF5/kglobalaccel_version.h
./KF5/KGlobalAccel/kglobalaccel_version.h

KF5/kglobalaccel_version.h has 5.78 while the latter 5.91 and plasma-desktop was using the former header file