Update existing tests.

libsolidity/ast/AST.cpp

@@ -292,7 +292,7 @@ bool FunctionDefinition::libraryFunction() const
 Visibility FunctionDefinition::defaultVisibility() const
 {
 	solAssert(!isConstructor(), "");
-	return Declaration::defaultVisibility();
+	return isFree() ? Visibility::Internal : Declaration::defaultVisibility();
 }
 
 FunctionTypePointer FunctionDefinition::functionType(bool _internal) const

libsolidity/ast/AST.h

@@ -852,9 +852,6 @@ public:
 		ContractDefinition const* _searchStart = nullptr
 	) const override;
 
-protected:
-	Visibility defaultVisibility() const override { return isFree() ? Visibility::Internal : Visibility::Public; }
-
 private:
 	StateMutability m_stateMutability;
 	bool m_free;