Remove deprecated host functions (#5038)

Sadly we need to keep one function `ext_blake2_256`. This function is
manually defined in `sp-core`.

substrate/client/executor/src/lib.rs

@@ -29,11 +29,8 @@
 #![warn(missing_docs)]
 #![recursion_limit="128"]
 
-#[macro_use]
-mod wasm_utils;
 #[macro_use]
 mod native_executor;
-pub mod deprecated_host_interface;
 mod wasm_runtime;
 #[cfg(test)]
 mod integration_tests;