[X86][NFC] Remove duplicate X86ELFObjectWriter class

[thegameg]

Summary

• lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp:

The X86ELFObjectWriter class is implemented in
lib/Target/X86/MCTargetDesc/X86ELFObjectWriter.cpp now.
The one in X86AsmBackend.cpp is not used anymore.

lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp

 
 namespace {
 
-class X86ELFObjectWriter : public MCELFObjectTargetWriter {
-public:
-  X86ELFObjectWriter(bool is64Bit, uint8_t OSABI, uint16_t EMachine,
-                     bool HasRelocationAddend, bool foobar)
-    : MCELFObjectTargetWriter(is64Bit, OSABI, EMachine, HasRelocationAddend) {}
-};
-
 class X86AsmBackend : public MCAsmBackend {
   const StringRef CPU;
   bool HasNopl;