Revert "operand: Implement operand hashing and use hashed set for declarations"

This reverts commit 1e665afa36.

src/literal_number.h

@@ -6,7 +6,6 @@
 
 #pragma once
 
-#include <cstddef>
 #include <cstring>
 #include <typeindex>
 #include "operand.h"
@@ -24,8 +23,6 @@ public:
 
     bool operator==(const Operand& other) const override;
 
-    std::size_t Hash() const override;
-
     template <typename T>
     static LiteralNumber* Create(T value) {
         static_assert(sizeof(T) == 4 || sizeof(T) == 8);