Remove the "headless" feature entirely

.travis.yml

@@ -18,7 +18,6 @@ env:
 script:
   - cargo build --verbose
   - cargo test --verbose
-  - cargo test --verbose --features "headless" --no-default-features
 
 os:
   - linux

Cargo.toml

@@ -13,7 +13,6 @@ build = "build.rs"
 [features]
 default = ["window"]
 window = []
-headless = []
 
 [dependencies]
 gl_common = "*"

appveyor.yml

@@ -9,5 +9,4 @@ install:
 build: false
 
 test_script:
-  - cargo test --verbose --no-default-features --features "window"
-  - cargo test --verbose --no-default-features --features "headless"
+  - cargo test --verbose

src/lib.rs

@@ -53,7 +53,6 @@ extern crate glutin_core_graphics as core_graphics;
 extern crate x11;
 
 pub use events::*;
-#[cfg(feature = "headless")]
 pub use headless::{HeadlessRendererBuilder, HeadlessContext};
 #[cfg(feature = "window")]
 pub use window::{WindowBuilder, Window, WindowProxy, PollEventsIterator, WaitEventsIterator};
@@ -65,7 +64,6 @@ pub use native_monitor::NativeMonitorId;
 mod api;
 mod platform;
 mod events;
-#[cfg(feature = "headless")]
 mod headless;
 #[cfg(feature = "window")]
 mod window;