JavaScript APIs from "runtime/js/40_files.js" combined abstractions
for stdio streams ("Stdout", "Stderr", "Stdin") and file system file
("File", "FsFile"). APIs from "runtime/js/40_read_file.js" and
"runtime/js/40_write_file.js" were implemented using ops from
"runtime/ops/fs.rs".
This file was removed and relevant APIs were moved to "deno_io/12_io.js"
and "runtime/js/30_fs.js".
This work is meant to enable factoring out "deno_fs" crate.