Support `deps.ts` (or drop replacement for `import_map.json`)

[bitsnaps]

Hi,

I thought import_map.json is the old way of Deno to manage dependencies, now it's deps.ts/dev_deps.ts (with -D flag) if I'm not wrong about that... I feel like it's the natural way of managing dependencies, so deno can cooperate with trex to make things easier.