Remove observers in clearBinding method REVERT

This reverts commit bfbcce99335a7bb4125b5b2041c2e246abb77178, reversing
changes made to ff926efa381a376de48d97d522430aa9e129b361.

client/android/div/src/main/java/com/yandex/div/core/expression/ExpressionsRuntime.kt

@@ -13,7 +13,6 @@ internal class ExpressionsRuntime(
 
     fun clearBinding() {
         triggersController.clearBinding()
-        variableController.removeGlobalObservers()
     }
 
     fun onAttachedToWindow(view: DivViewFacade) {

client/android/div/src/main/java/com/yandex/div/core/expression/variables/VariableController.kt

@@ -7,6 +7,7 @@ import com.yandex.div.core.view2.errors.ErrorCollector
 import com.yandex.div.data.Variable
 import com.yandex.div.data.VariableDeclarationException
 import com.yandex.div.internal.Assert
+
 import com.yandex.div.json.missingVariable
 
 @Mockable
@@ -17,7 +18,6 @@ internal class VariableController {
 
     private var onAnyVariableChangeCallback: ((Variable) -> Unit)? = null
     private val notifyVariableChangedCallback = { v : Variable -> notifyVariableChanged(v) }
-    private val notifyVariableDeclaredCallback = { v : Variable -> onVariableDeclared(v) }
 
     private fun addObserver(name: String, observer: (Variable) -> Unit) {
         val observers = onChangeObservers.getOrPut(name) {
@@ -92,7 +92,7 @@ internal class VariableController {
      */
     fun addSource(source: VariableSource) {
         source.observeVariables(notifyVariableChangedCallback)
-        source.observeDeclaration(notifyVariableDeclaredCallback)
+        source.observeDeclaration { onVariableDeclared(it) }
         extraVariablesSources.add(source)
     }
 
@@ -129,11 +129,4 @@ internal class VariableController {
         Assert.assertNull(onAnyVariableChangeCallback)
         onAnyVariableChangeCallback = callback
     }
-
-    fun removeGlobalObservers() {
-        extraVariablesSources.forEach {
-            it.removeOnChangeObserver(notifyVariableChangedCallback)
-            it.removeDeclarationObserver(notifyVariableDeclaredCallback)
-        }
-    }
 }

client/android/div/src/main/java/com/yandex/div/core/expression/variables/VariableSource.kt

@@ -25,14 +25,4 @@ internal class VariableSource(
             it.addObserver(observer)
         }
     }
-
-    internal fun removeOnChangeObserver(observer: (Variable) -> Unit) {
-        variables.values.forEach {
-            it.removeObserver(observer)
-        }
-    }
-
-    internal fun removeDeclarationObserver(observer: (Variable) -> Unit) {
-        declarationObservers.remove(observer)
-    }
 }