Consistent recommendations for deno.json/import-maps in edge functions

# Improve documentation ## Link [https://supabase.com/docs/guides/functions/development-tips#organizing-your-edge-functions](https://supabase.com/docs/guides/functions/development-tips#organizing-your-edge-functions) ## Describe the problem In this part of the documentation, a file structure is recommended which makes note of a top-level import map. This is however explicitly not recommend as noted [here](https://supabase.com/docs/guides/functions/dependencies#using-denojson-recommended). Instead, `deno.json` files should be used for each function, using import maps is legacy according to the docs. ## Describe the improvement Remove the `import_map.json` from the recommended file structure and instead show `deno.json` files for each function, as is currently recommended.