fix: Don't delete existing `.git` when using `--no-git` flag (#12968)
## Why
Closes #12967. Users who pass `--no-git` expect create-turbo to leave
git alone, not initialize a repo or delete an existing `.git` directory.
## What
Stops the `--no-git` path from doing any git work and removes the
now-unused `.git` deletion helper.
## How
Adds coverage that `--no-git` does not call the git init helper or spawn
git commands, while preserving normal git initialization when the flag
is not used.
Verified with:
- `pnpm --filter create-turbo test -- --runTestsByPath
__tests__/git.test.ts __tests__/index.test.ts`
- `pnpm --filter create-turbo check-types`