Remove dependency to @std/http/unstable-route in deno init --serve

[kt3k]

route in @std/http package is unstable, and shouldn't be considered to be working in the future.

Actually now a breaking change is suggested for improving the ergonomics ( ref: denoland/std#6094 ), but the dependency to it from deno init --serve prevents it.

I suggest we temporarily remove the dependency to it until it becomes stable, and I suggest replacing it with simple inline implementation using URLPattern directly in deno init output. What do you think?