mruby-io does not provide to_path method for implicit conversion

mruby does not use implicit type conversion by `to_xxx` (e.g. to_int,
to_str, etc.)

mrbgems/mruby-io/README.md

@@ -165,7 +165,7 @@ Add the line below to your build configuration.
 | File#flock                  | o        |          |
 | File#lstat                  |          |          |
 | File#mtime                  |          |          |
-| File#path, File#to_path     | o        |          |
+| File#path                   | o        |          |
 | File#size                   |          |          |
 | File#truncate               |          |          |
 

mrbgems/mruby-io/mrblib/file.rb

@@ -199,8 +199,6 @@ class File < IO
   def self.path(filename)
     if filename.kind_of?(String)
       filename
-    elsif filename.respond_to?(:to_path)
-      filename.to_path
     else
       raise TypeError, "no implicit conversion of #{filename.class} into String"
     end