Remove unnecessary freeing functions

`rbs_node_destroy`, `rbs_hash_free`, `rbs_node_list_free` are only
calling each other recursively without any real freeing logic.

This is the result of previous efforts to allocate all nodes on the
arena. So we don't need these functions anymore.

Author: st0012

ext/rbs_extension/main.c

@@ -125,7 +125,6 @@ static VALUE parse_type_try(VALUE a) {
 
 
   VALUE ruby_ast = rbs_struct_to_ruby_value(ctx, type);
-  rbs_node_destroy((rbs_node_t *) type);
   return ruby_ast;
 }
 
@@ -214,7 +213,6 @@ static VALUE parse_method_type_try(VALUE a) {
   );
 
   VALUE ruby_ast = rbs_struct_to_ruby_value(ctx, (rbs_node_t *) method_type);
-  rbs_node_destroy((rbs_node_t *) method_type);
   return ruby_ast;
 }
 
@@ -255,7 +253,6 @@ static VALUE parse_signature_try(VALUE a) {
   );
 
   VALUE ruby_ast = rbs_struct_to_ruby_value(ctx, (rbs_node_t *) signature);
-  rbs_node_destroy((rbs_node_t *) signature);
   return ruby_ast;
 }
 

include/rbs/ast.h

@@ -685,6 +685,4 @@ rbs_types_union_t *rbs_types_union_new(rbs_allocator_t *allocator, rbs_location_
 rbs_types_untyped_function_t *rbs_types_untyped_function_new(rbs_allocator_t *allocator, rbs_location_t *location, rbs_node_t *return_type);
 rbs_types_variable_t *rbs_types_variable_new(rbs_allocator_t *allocator, rbs_location_t *location, rbs_ast_symbol_t *name);
 
-void rbs_node_destroy(rbs_node_t *any_node);
-
 #endif