[NVPTX] Remove extraneous initializeNVVMReflectLegacyPassPass declaration (#135825)

This was already declared in NVPTX.h and I accidentally added it back in
#134416.

Author: YonahGoldberg

llvm/lib/Target/NVPTX/NVVMReflect.cpp

@@ -52,10 +52,6 @@ using namespace llvm;
 
 #define DEBUG_TYPE "nvvm-reflect"
 
-namespace llvm {
-void initializeNVVMReflectLegacyPassPass(PassRegistry &);
-} // namespace llvm
-
 namespace {
 class NVVMReflect {
   // Map from reflect function call arguments to the value to replace the call