Revert "cgo: set cgo compiler flags in backend.go"

This reverts commit 09416b1d.

required pkg-config .pc files are not provided by the qt project
on linux the distribution packages contains them but on  windows
and macOS these are not available causing build to fail

ref: https://bugreports.qt.io/browse/QTBUG-86080

gui/backend.go

@@ -3,8 +3,6 @@ package main
 /* a wrapper around bitmask that exposes status to a QtQml gui.
    Have a look at the pkg/backend module for further enlightment. */
 
-// #cgo pkg-config: Qt6Core Qt6Gui Qt6Widgets Qt6Quick Qt6QuickControls2
-// #cgo CXXFLAGS: -I ..
 import "C"
 
 import "unsafe"