Remove `format.sh` as it's been unsupported >70 days (#15884)

Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

format.sh

-#!/bin/bash
-
-echo "vLLM linting system has been moved from format.sh to pre-commit hook."
-echo "Please run 'pip install -r requirements/lint.txt', followed by"
-echo "'pre-commit install --hook-type pre-commit --hook-type commit-msg' to install the pre-commit hook."
-echo "Then linters will run automatically before each commit."