[OpenMP][deviceRTLs] Remove omp_is_initial_device

[tianshilei1992]

Summary

omp_is_initial_device in device code was implemented as a builtin
function in D38968 for a better performance. Therefore there is no chance that
this function will be called to deviceRTLs. As we're moving to build deviceRTLs
with OpenMP compiler, this function can lead to a compilation error. This patch
just simply removes it.

[JonChesterfield]

Yep, thanks. When we replace the builtin with something using variant, we can reinstate this. Until then, & doesn't work anyway.

openmp/libomptarget/deviceRTLs/common/src/libcall.cu

 }
 
 EXTERN int omp_get_team_num() {
   int rc = GetOmpTeamId();
   PRINT(LD_IO, "call omp_get_team_num() returns %d\n", rc);
   return rc;
 }
 
-EXTERN int omp_is_initial_device(void) {
-  PRINT0(LD_IO, "call omp_is_initial_device() returns 0\n");
-  return 0; // 0 by def on device
-}
-
 // Unspecified on the device.
 EXTERN int omp_get_initial_device(void) {
   PRINT0(LD_IO, "call omp_get_initial_device() returns 0\n");
   return 0;
 }
 
 // Unused for now.
 EXTERN int omp_get_max_task_priority(void) {

openmp/libomptarget/deviceRTLs/interface.h

 EXTERN void omp_set_schedule(omp_sched_t kind, int modifier);
 EXTERN omp_proc_bind_t omp_get_proc_bind(void);
 EXTERN int omp_get_cancellation(void);
 EXTERN void omp_set_default_device(int deviceId);
 EXTERN int omp_get_default_device(void);
 EXTERN int omp_get_num_devices(void);
 EXTERN int omp_get_num_teams(void);
 EXTERN int omp_get_team_num(void);
-EXTERN int omp_is_initial_device(void);
 EXTERN int omp_get_initial_device(void);
 EXTERN int omp_get_max_task_priority(void);
 
 ////////////////////////////////////////////////////////////////////////////////
 // file below is swiped from kmpc host interface
 ////////////////////////////////////////////////////////////////////////////////
 
 ////////////////////////////////////////////////////////////////////////////////