message: [XLA] Remove some unused friend declarations from XlaBuilder.
  The free xla::Constant* functions all call the free xla::ConstantLiteral function, not XlaBuilder itself.
diff: @@ -692,48 +692,6 @@ class XlaBuilder {
  const Shape& shape, const string& name);
  friend XlaOp ConstantLiteral(XlaBuilder* builder,
  const LiteralSlice& literal);
  - template <typename NativeT>
  - friend XlaOp ConstantR0(XlaBuilder* builder, NativeT value);
  - template <typename NativeT>
  - friend XlaOp ConstantR1(XlaBuilder* builder,
  - absl::Span<const NativeT> values);
  - friend XlaOp ConstantR1(XlaBuilder* builder,
  - const tensorflow::core::Bitmap& values);
  - template <typename NativeT>
  - friend XlaOp ConstantR2(
  - XlaBuilder* builder,
  - std::initializer_list<std::initializer_list<NativeT>> values);
  - template <typename NativeT>
  - friend XlaOp ConstantFromArrayWithLayout(XlaBuilder* builder,
  - const Array<NativeT>& values,
  - const Layout& layout);
  - template <typename NativeT>
  - friend XlaOp ConstantFromArray(XlaBuilder* builder,
  - const Array<NativeT>& values);
  - template <typename NativeT>
  - friend XlaOp ConstantR2FromArray2DWithLayout(XlaBuilder* builder,
  - const Array2D<NativeT>& values,
  - const Layout& layout);
  - template <typename NativeT>
  - friend XlaOp ConstantR2FromArray2D(XlaBuilder* builder,
  - const Array2D<NativeT>& values);
  - template <typename NativeT>
  - friend XlaOp ConstantR3FromArray3DWithLayout(XlaBuilder* builder,
  - const Array3D<NativeT>& values,
  - const Layout& layout);
  - template <typename NativeT>
  - friend XlaOp ConstantR3FromArray3D(XlaBuilder* builder,
  - const Array3D<NativeT>& values);
  - template <typename NativeT>
  - friend XlaOp ConstantR4FromArray4DWithLayout(XlaBuilder* builder,
  - const Array4D<NativeT>& values,
  - const Layout& layout);
  - template <typename NativeT>
  - friend XlaOp ConstantR4FromArray4D(XlaBuilder* builder,
  - const Array4D<NativeT>& values);
  -
  - template <typename NativeT>
  - friend XlaOp ConstantR1(XlaBuilder* builder, int64 length, NativeT value);
  friend XlaOp Broadcast(const XlaOp& operand,
  absl::Span<const int64> broadcast_sizes);
  