Delete check that ReadValue/Assign operations have to be in pair in o…

…v::Model (openvinotoolkit#23051)

### Details:
If ReadValue and Assign are not paired in model topology we have "Model
is incorrect. Assign and ReadValue operations must be in pairs on the
network."

Check for ReadValue-Assign pairs is useless and it is an obstacle for
model transformation debugging. Moreover, with more advanced techniques
of state modification there can be other ops (custom ones) that modify
state in place.

### Tickets:
 - *CVS-133159*

src/core/src/model.cpp

@@ -220,11 +220,6 @@ void ov::Model::prerequirements(bool detect_variables, bool detect_parameters) {
 void ov::Model::validate_nodes_and_infer_types() const {
     OV_ITT_SCOPED_TASK(ov::itt::domains::core, "Model::validate_nodes_and_infer_types");
 
-    struct Counter {
-        int cnt_assign = 0;
-        int cnt_read_val = 0;
-    };
-    std::map<ov::op::util::Variable*, Counter> pair_checker;
     std::stringstream unregistered_parameters;
     std::stringstream unregistered_variables;
     std::unordered_set<const ov::descriptor::Tensor*> tensors;
@@ -246,12 +241,6 @@ void ov::Model::validate_nodes_and_infer_types() const {
         if (variable_op &&
             std::find(m_variables.begin(), m_variables.end(), variable_op->get_variable()) == m_variables.end())
             unregistered_variables << variable_op->get_variable_id() << std::endl;
-
-        if (const auto& assign = std::dynamic_pointer_cast<ov::op::util::AssignBase>(node)) {
-            pair_checker[assign->get_variable().get()].cnt_assign++;
-        } else if (const auto& read_value = std::dynamic_pointer_cast<ov::op::util::ReadValueBase>(node)) {
-            pair_checker[read_value->get_variable().get()].cnt_read_val++;
-        }
     }
 
     OPENVINO_ASSERT(unregistered_parameters.str().empty(),
@@ -261,13 +250,7 @@ void ov::Model::validate_nodes_and_infer_types() const {
     OPENVINO_ASSERT(unregistered_variables.str().empty(),
                     "Model references undeclared Variables: ",
                     unregistered_variables.str());
-    bool only_pairs =
-        std::all_of(pair_checker.begin(), pair_checker.end(), [](const std::pair<op::util::Variable*, Counter>& val) {
-            return val.second.cnt_assign == 1 && val.second.cnt_read_val == 1;
-        });
-    OPENVINO_ASSERT(only_pairs,
-                    "Model is incorrect. Assign and ReadValue operations must be in pairs on the "
-                    "network.");
+
     for (const auto& output : outputs()) {
         OPENVINO_ASSERT(ov::layout::utils::is_compatible(ov::layout::get_layout(output), output.get_partial_shape()),
                         "Result '",