Fix compile error

'NSEventMask', 'NSEventModifierFlags' are not module, so commands like
below is not valid anymore.

    pub use self::NSEventMask::*;
    pub use self::NSEventModifierFlags::*;

src/appkit.rs

@@ -19,8 +19,6 @@ pub use self::NSBackingStoreType::*;
 pub use self::NSOpenGLPixelFormatAttribute::*;
 pub use self::NSOpenGLPFAOpenGLProfiles::*;
 pub use self::NSEventType::*;
-pub use self::NSEventMask::*;
-pub use self::NSEventModifierFlags::*;
 
 use std::ffi::CString;