MCExpr: Remove error-prone operator<<

Printing an expression is error-prone without a MCAsmInfo argument.
The callers have migrated to MCAsmInfo::printExpr or MCExpr::print.

llvm/include/llvm/MC/MCExpr.h

@@ -134,11 +134,6 @@ public:
                                            MCValue &);
 };
 
-inline raw_ostream &operator<<(raw_ostream &OS, const MCExpr &E) {
-  E.print(OS, nullptr);
-  return OS;
-}
-
 ////  Represent a constant integer expression.
 class MCConstantExpr : public MCExpr {
   int64_t Value;

llvm/lib/Target/CSKY/AsmParser/CSKYAsmParser.cpp

@@ -441,10 +441,10 @@ public:
 
     switch (Kind) {
     case CPOP:
-      OS << *getConstpoolOp();
+      MAI.printExpr(OS, *getConstpoolOp());
       break;
     case Immediate:
-      OS << *getImm();
+      MAI.printExpr(OS, *getImm());
       break;
     case KindTy::Register:
       OS << "<register " << RegName(getReg()) << ">";