[clang][ExtractAPI] Fix -Wpessimizing-move in DeclarationFragments.h (NFC)

/Users/jiefu/llvm-project/clang/include/clang/ExtractAPI/DeclarationFragments.h:118:26: error: moving a temporary object prevents copy elision [-Werror,-Wpessimizing-move]
    Fragments.insert(It, std::move(Fragment(Spelling, Kind, PreciseIdentifier,
                         ^
/Users/jiefu/llvm-project/clang/include/clang/ExtractAPI/DeclarationFragments.h:118:26: note: remove std::move call here
    Fragments.insert(It, std::move(Fragment(Spelling, Kind, PreciseIdentifier,
                         ^~~~~~~~~~
1 error generated.