Fix warning and directory restructure.

substrate/pwasm-alloc/build.rs

@@ -1,14 +0,0 @@
-//! Set a nightly feature
-
-extern crate rustc_version;
-use rustc_version::{version, version_meta, Channel};
-
-fn main() {
-    // Assert we haven't travelled back in time
-    assert!(version().unwrap().major >= 1);
-
-    // Set cfg flags depending on release channel
-    if let Channel::Nightly = version_meta().unwrap().channel {
-        println!("cargo:rustc-cfg=feature=\"nightly\"");
-    }
-}