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

crates/nu_plugin_sys/Cargo.toml

@@ -27,4 +27,3 @@ version = "0.1.0-beta.3"
 features = ["host", "cpu", "memory", "disk", "net", "sensors"]
 
 [build-dependencies]
-nu-build = {version = "0.17.0", path = "../nu-build"}

crates/nu_plugin_sys/build.rs

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