Remove the check for unstable features

We don't use nightly Rust anymore, nor do we try to land docs for
features while they're still unstable, so this check is no longer
needed. The tests will just fail if we try to use a feature flag in code
listings.

ci/build.sh

@@ -4,13 +4,6 @@ set -e
 
 export PATH=$PATH:/home/travis/.cargo/bin;
 
-# Feature check
-cd ci/stable-check
-
-cargo run -- ../../src
-
-cd ../..
-
 echo 'Spellchecking...'
 bash ci/spellcheck.sh list
 echo 'Testing...'

ci/stable-check/Cargo.lock

@@ -1,4 +0,0 @@
-[root]
-name = "stable-check"
-version = "0.1.0"
-

ci/stable-check/Cargo.toml

@@ -1,6 +0,0 @@
-[package]
-name = "stable-check"
-version = "0.1.0"
-authors = ["steveklabnik <steve@steveklabnik.com>"]
-
-[dependencies]

ci/stable-check/src/main.rs

@@ -1,43 +0,0 @@
-use std::error::Error;
-use std::env;
-use std::fs;
-use std::fs::File;
-use std::io::prelude::*;
-use std::path::Path;
-
-fn main() {
-    let arg = env::args().nth(1).unwrap_or_else(|| {
-        println!("Please pass a src directory as the first argument");
-        std::process::exit(1);
-    });
-
-    match check_directory(&Path::new(&arg)) {
-        Ok(()) => println!("passed!"),
-        Err(e) => {
-            println!("Error: {}", e);
-            std::process::exit(1);
-        }
-    }
-
-}
-
-fn check_directory(dir: &Path) -> Result<(), Box<Error>> {
-    for entry in fs::read_dir(dir)? {
-        let entry = entry?;
-        let path = entry.path();
-
-        if path.is_dir() {
-            continue;
-        }
-
-        let mut file = File::open(&path)?;
-        let mut contents = String::new();
-        file.read_to_string(&mut contents)?;
-
-        if contents.contains("#![feature") {
-            return Err(From::from(format!("Feature flag found in {:?}", path)));
-        }
-    }
-
-    Ok(())
-}