Drop the class wrapper from the C++20 comparison operator signatures in the docs

The signature boxes of operator<=> and the C++20 half of operator== wrapped
the member declarations in an incomplete "class basic_json { ... };". The
trailing const already marks them as members, and no other page uses such a
wrapper.

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

docs/mkdocs/docs/api/basic_json/operator_eq.md

@@ -11,12 +11,10 @@ template<typename ScalarType>
 bool operator==(ScalarType lhs, const const_reference rhs) noexcept(/* see below */); // (2)
 
 // since C++20
-class basic_json {
-    bool operator==(const_reference rhs) const noexcept;              // (1)
+bool operator==(const_reference rhs) const noexcept;             // (1)
 
-    template<typename ScalarType>
-    bool operator==(ScalarType rhs) const noexcept(/* see below */); // (2)
-};
+template<typename ScalarType>
+bool operator==(ScalarType rhs) const noexcept(/* see below */); // (2)
 ```
 
 1. Compares two JSON values for equality according to the following rules:

docs/mkdocs/docs/api/basic_json/operator_spaceship.md

@@ -2,12 +2,10 @@
 
 ```cpp
 // since C++20
-class basic_json {
-    std::partial_ordering operator<=>(const_reference rhs) const noexcept;  // (1)
+std::partial_ordering operator<=>(const_reference rhs) const noexcept;                   // (1)
 
-    template<typename ScalarType>
-    std::partial_ordering operator<=>(const ScalarType rhs) const noexcept(/* see below */); // (2)
-};
+template<typename ScalarType>
+std::partial_ordering operator<=>(const ScalarType rhs) const noexcept(/* see below */); // (2)
 ```
 
 1. 3-way compares two JSON values producing a result of type `std::partial_ordering` according to the following rules: