build: remove entt library

include/entt/poly/fwd.hpp

@@ -1,21 +0,0 @@
-#ifndef ENTT_POLY_FWD_HPP
-#define ENTT_POLY_FWD_HPP
-
-#include "../stl/cstddef.hpp"
-
-namespace entt {
-
-// NOLINTNEXTLINE(cppcoreguidelines-avoid-c-arrays, modernize-avoid-c-arrays)
-template<typename, stl::size_t Len = sizeof(double[2]), stl::size_t = alignof(double[2])>
-class basic_poly;
-
-/**
- * @brief Alias declaration for the most common use case.
- * @tparam Concept Concept descriptor.
- */
-template<typename Concept>
-using poly = basic_poly<Concept>;
-
-} // namespace entt
-
-#endif