Remove unused devDependency 'prettier-config-standard'

[trivikr]

Fixes: #3014

make fmt is successful, and no files were updated

$ make fmt
pnpm format

> [email protected] format /Users/trivikram/workspace/atproto
> pnpm lint:fix && pnpm style:fix


> [email protected] lint:fix /Users/trivikram/workspace/atproto
> pnpm lint --fix


> [email protected] lint /Users/trivikram/workspace/atproto
> eslint . --ext .ts,.js "--fix"
...
tsconfig/nodenext.json 0ms (unchanged)
tsconfig/tests.json 0ms (unchanged)

$ git status
On branch remove-prettier-config-standard
nothing to commit, working tree clean