Remove TypeSystemContext::mayBeTypeVariable optimization

It doesn't work now since anyway it's required to obtain type
constructor
At the same time, now it's not very expensive to obtain the constructor
since it's just a lookup tag

core/descriptors/src/org/jetbrains/kotlin/types/checker/ClassicTypeSystemContext.kt

@@ -401,10 +401,6 @@ interface ClassicTypeSystemContext : TypeSystemInferenceExtensionContext, TypeSy
         errorSupportedOnlyInTypeInference()
     }
 
-    override fun KotlinTypeMarker.mayBeTypeVariable(): Boolean {
-        errorSupportedOnlyInTypeInference()
-    }
-
     override fun CapturedTypeMarker.typeConstructorProjection(): TypeArgumentMarker {
         require(this is NewCapturedType, this::errorMessage)
         return this.constructor.projection

core/type-system/src/org/jetbrains/kotlin/types/model/TypeSystemContext.kt

@@ -155,8 +155,6 @@ interface TypeSystemInferenceExtensionContext : TypeSystemContext, TypeSystemBui
 
     fun TypeVariableMarker.freshTypeConstructor(): TypeConstructorMarker
 
-    fun KotlinTypeMarker.mayBeTypeVariable(): Boolean
-
     fun CapturedTypeMarker.typeConstructorProjection(): TypeArgumentMarker
     fun CapturedTypeMarker.typeParameter(): TypeParameterMarker?
     fun CapturedTypeMarker.withNotNullProjection(): KotlinTypeMarker