Remove build.rs and nu-build (#2282)

crates/nu-source/Cargo.toml

@@ -18,4 +18,3 @@ serde = {version = "1.0.114", features = ["derive"]}
 termcolor = "1.1.0"
 
 [build-dependencies]
-nu-build = {version = "0.17.0", path = "../nu-build"}

crates/nu-source/build.rs

@@ -1,3 +0,0 @@
-fn main() -> Result<(), Box<dyn std::error::Error>> {
-    nu_build::build()
-}