remove linux_headless/appimage/flatpak feature

src/flutter_ffi.rs

@@ -774,8 +774,7 @@ pub fn main_get_error() -> String {
 }
 
 pub fn main_show_option(_key: String) -> SyncReturn<bool> {
-    #[cfg(all(target_os = "linux", feature = "linux_headless"))]
-    #[cfg(not(any(feature = "flatpak", feature = "appimage")))]
+    #[cfg(target_os = "linux")]
     if _key.eq(config::CONFIG_OPTION_ALLOW_LINUX_HEADLESS) {
         return SyncReturn(true);
     }