Revert plugins.

src/lib.rs

@@ -79,10 +79,6 @@ pub mod fn_native;
 mod fn_register;
 mod module;
 mod optimize;
-#[cfg(not(feature = "no_module"))]
-pub mod plugin;
-#[cfg(feature = "no_module")]
-mod plugin;
 pub mod packages;
 mod parser;
 mod result;
@@ -96,7 +92,6 @@ pub use any::Dynamic;
 pub use engine::Engine;
 pub use error::{ParseError, ParseErrorType};
 pub use fn_register::{RegisterFn, RegisterResultFn};
-pub use fn_register::RegisterPlugin;
 pub use module::Module;
 pub use parser::{ImmutableString, AST, INT};
 pub use result::EvalAltResult;