Rollup merge of #150761 - rm-unneded-test, r=wesleywiser

rustc book: fix grammar

It was added in ddee45e ([here](https://github.com/rust-lang/rust/pull/97802/changes#diff-85dc642a7bdad363a9e37d2491230280fcd977391ba7a242bda2da9ddb55f654) to be specific) when SIGPIPE was controlled with an attribute on `fn main()` which meant it could also be combined with `#[rustc_main]`:

    #[unix_sigpipe = "sig_dfl"]
    #[rustc_main]
    fn rustc_main() {

The test stopped being needed in cde0cde when `#[unix_sigpipe = "..."]` was replaced by `-Zon-broken-pipe=...`. And it will not be needed when `-Zon-broken-pipe=...` is replaced by an Externally Implementable Item (see #150591). Let's remove this test.

Tracking issue:
- #150588

Author: Kobzol