Remove priority from attribute constructor/destructor
On some platforms, the attribute constructor and destructor won't take priorities and the compilation failed. On such platform would be macOS. For this reason, the constructor/destructor in the libisc was reworked to not use priorities, but have a single constructor and destructor that calls the appropriate routines in correct order.
This commit removes the extra priority because it's now not needed and it also breaks a compilation on macOS with GCC 10.
(cherry picked from commit d68b009c)
Closes #2708 (closed)