[Hexagon] Remove chksetELFHeaderEFlags (NFC)

The function was introduced without any use on Nov 9, 2015 in commit
7cd0892729.

llvm/lib/Target/Hexagon/AsmParser/HexagonAsmParser.cpp

@@ -141,12 +141,6 @@ class HexagonAsmParser : public MCTargetAsmParser {
   int processInstruction(MCInst &Inst, OperandVector const &Operands,
                          SMLoc IDLoc);
 
-  // Check if we have an assembler and, if so, set the ELF e_header flags.
-  void chksetELFHeaderEFlags(unsigned flags) {
-    if (getAssembler())
-      getAssembler()->setELFHeaderEFlags(flags);
-  }
-
   unsigned matchRegister(StringRef Name);
 
 /// @name Auto-generated Match Functions