[Libomptarget] Remove undefined symbol in old runtime

A function with no definition was left in the old runtime, causing
linker errors when trying to compile.

Reviewed By: tianshilei1992

Differential Revision: https://reviews.llvm.org/D114264

GitOrigin-RevId: fbfe8fcbc31d492d5538c09782b787bba89d01e5

libomptarget/deviceRTLs/target_interface.h

diff --git a/libomptarget/deviceRTLs/target_interface.h b/libomptarget/deviceRTLs/target_interface.h
index 94c92eb..cf65197 100644
--- a/libomptarget/deviceRTLs/target_interface.h
+++ b/libomptarget/deviceRTLs/target_interface.h
@@ -25,7 +25,6 @@
 EXTERN NOINLINE int __kmpc_get_hardware_num_threads_in_block();
 EXTERN unsigned __kmpc_get_warp_size();
 EXTERN unsigned GetWarpId();
-EXTERN unsigned GetWarpSize();
 EXTERN unsigned GetLaneId();
 
 // Atomics