removed old, unused build.rs (#7614)

Cargo.toml

@@ -4,7 +4,6 @@ name = "parity"
 version = "1.10.0"
 license = "GPL-3.0"
 authors = ["Parity Technologies <admin@parity.io>"]
-build = "build.rs"
 
 [dependencies]
 log = "0.3"

build.rs

@@ -1,35 +0,0 @@
-// Copyright 2015-2017 Parity Technologies (UK) Ltd.
-// This file is part of Parity.
-
-// Parity is free software: you can redistribute it and/or modify
-// it under the terms of the GNU General Public License as published by
-// the Free Software Foundation, either version 3 of the License, or
-// (at your option) any later version.
-
-// Parity is distributed in the hope that it will be useful,
-// but WITHOUT ANY WARRANTY; without even the implied warranty of
-// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-// GNU General Public License for more details.
-
-// You should have received a copy of the GNU General Public License
-// along with Parity.  If not, see <http://www.gnu.org/licenses/>.
-
-extern crate rustc_version;
-
-const MIN_RUSTC_VERSION: &'static str = "1.15.1";
-
-fn main() {
-	let is = rustc_version::version().unwrap();
-	let required = MIN_RUSTC_VERSION.parse().unwrap();
-	assert!(is >= required, format!("
-
-It looks like you are compiling Parity with an old rustc compiler {}.
-Parity requires version {}. Please update your compiler.
-If you use rustup, try this:
-
-    rustup update stable
-
-and try building Parity again.
-
-", is, required));
-}