Remove priority from attribute constructor/destructor

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.