AST: Remove unused TypeBase::isAssignableType()

Author: slavapestov

include/swift/AST/Types.h

@@ -651,11 +651,6 @@ class alignas(1 << TypeAlignInBits) TypeBase {
     return getRecursiveProperties().hasDependentMember();
   }
 
-  /// Check if this type is a valid type for the LHS of an assignment.
-  /// This mainly means hasLValueType(), but empty tuples and tuples of empty
-  /// tuples also qualify.
-  bool isAssignableType();
-
   /// isExistentialType - Determines whether this type is an existential type,
   /// whose real (runtime) type is unknown but which is known to conform to
   /// some set of protocols. Protocol and protocol-conformance types are

lib/AST/Type.cpp

@@ -543,19 +543,6 @@ bool TypeBase::isBool() {
   return false;
 }
 
-
-bool TypeBase::isAssignableType() {
-  if (hasLValueType()) return true;
-  if (auto tuple = getAs<TupleType>()) {
-    for (auto eltType : tuple->getElementTypes()) {
-      if (!eltType->isAssignableType())
-        return false;
-    }
-    return true;
-  }
-  return false;
-}
-
 Type TypeBase::getRValueType() {
   // If the type is not an lvalue, this is a no-op.
   if (!hasLValueType())