Improved arch packaging

No need to bundle a .desktop file with arch source packages anymore.
dupeGuru's source package takes care of that.

pkg/arch/dupeguru.desktop

@@ -0,0 +1,8 @@
+[Desktop Entry]
+Name={longname}
+Comment=Find duplicate files.
+Exec={execname}
+Icon={iconpath}
+Terminal=false
+Type=Application
+Categories=Utility;