[Clang][LoongArch] Remove duplicate declaration. NFC

Author: wangleiat

clang/lib/Driver/ToolChains/Arch/LoongArch.h

@@ -20,12 +20,9 @@ namespace loongarch {
 void getLoongArchTargetFeatures(const Driver &D, const llvm::Triple &Triple,
                                 const llvm::opt::ArgList &Args,
                                 std::vector<llvm::StringRef> &Features);
+
 StringRef getLoongArchABI(const Driver &D, const llvm::opt::ArgList &Args,
                           const llvm::Triple &Triple);
-
-void getLoongArchTargetFeatures(const Driver &D, const llvm::Triple &Triple,
-                                const llvm::opt::ArgList &Args,
-                                std::vector<llvm::StringRef> &Features);
 } // end namespace loongarch
 } // end namespace tools
 } // end namespace driver