Prune a redundant include "RISCVISelDAGToDAG.h" (fixup for llvm#128978)

Seems it is not affected.

Author: chapuni

llvm/lib/Target/RISCV/MCA/RISCVCustomBehaviour.cpp

@@ -14,7 +14,6 @@
 #include "RISCVCustomBehaviour.h"
 #include "MCTargetDesc/RISCVMCTargetDesc.h"
 #include "RISCV.h"
-#include "RISCVISelDAGToDAG.h"
 #include "TargetInfo/RISCVTargetInfo.h"
 #include "llvm/MC/TargetRegistry.h"
 #include "llvm/Support/Debug.h"