Remove the unused legacy_discarded_value_comparison from abi_config

Nothing reads it: the view does not compare values.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

include/nlohmann/detail/abi_config.hpp

@@ -15,10 +15,11 @@ namespace detail
 {
 
 /*!
-@brief the configuration macros that change the library's behavior
+@brief the configuration macros that json_view.hpp reads
 
 json.hpp undefines these macros at its end (see macro_unscope.hpp), so code
-that builds on the library after it (json_view.hpp) reads them here. Like the
+that builds on the library after it (json_view.hpp) reads them here. A macro
+is added when the view starts to depend on it. Like the
 macros, they are part of the ABI namespace, so they always match the
 basic_json they are used with.
 */
@@ -26,8 +27,6 @@ struct abi_config
 {
     /// JSON_STRICT_NUL_HANDLING: a null byte is an error, not the end of input
     static constexpr bool strict_nul_handling = JSON_STRICT_NUL_HANDLING != 0;
-    /// JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON
-    static constexpr bool legacy_discarded_value_comparison = JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON != 0;
 };
 
 }  // namespace detail