Remove accelmath.h (#679)

This fixes compilation with NVHPC 21.9 in some cases.

* Update mod2c submodule with mod2c#73, which does the same thing there.
* Update nmodl submodule with nmodl#762, which fixes code generation for
  the SH_na8st.mod mechanism in the reduced_dentate model.

Author: olupton

coreneuron/sim/scopmath/crout_thread.cpp

@@ -42,10 +42,6 @@
 /*  Functions called: makevector(), freevector()		*/
 /*                                                              */
 /*--------------------------------------------------------------*/
-
-#if defined(__PGI) && defined(_OPENACC)
-#include "accelmath.h"
-#endif
 #include <cmath>
 #include "coreneuron/mechanism/mech/cfile/scoplib.h"
 #include "coreneuron/sim/scopmath/newton_struct.h"

coreneuron/sim/scopmath/sparse_thread.cpp

@@ -6,10 +6,6 @@
  *   Duke University
  *
  ******************************************************************************/
-
-#if defined(__PGI) && defined(_OPENACC)
-#include "accelmath.h"
-#endif
 #include <stdlib.h>
 #include "coreneuron/mechanism/mech/cfile/scoplib.h"
 #include "coreneuron/mechanism/mech/mod2c_core_thread.hpp" /* _threadargs, _STRIDE, etc. */