Instead of always using the temporary file /tmp/libupdatergtk.so generat...

...es a new name.

This solves a problem: if the file already existed and the current user
couldn't truncate it the auto update couldn't use the Gtk auto-updater.

In this commit it also deletes the file and avoids creating and closing
the file and opening again.

MD-20923
If extractFileFromBinary() is no longer opening the fd it shouldn't be closing it either, that should be moved up to the same function that opens the file.