Remove rust=rustc alias

I was asked to add this for backwards comparability when I renamed `rust`
to `rustc` and added `rustcMaster`. It has been a few months so I'd hope
deprecating this is acceptable.

pkgs/development/tools/rust/racer/default.nix

@@ -1,8 +1,4 @@
-{stdenv, fetchgit, rust, makeWrapper }:
-
-let
-  rustSrc = rust.src;
-in
+{stdenv, fetchgit, rustc, makeWrapper }:
 
 stdenv.mkDerivation rec {
   #TODO add emacs support
@@ -13,16 +9,16 @@ stdenv.mkDerivation rec {
     sha256 = "1159fsfca2kqvlajp8sawrskip7hc0rppk8vhwxa2vw8zznp56w0";
   };
 
-  buildInputs = [ rust makeWrapper ];
+  buildInputs = [ rustc makeWrapper ];
 
   installPhase = ''
     mkdir -p $out/bin
     cp -p bin/racer $out/bin/
-    wrapProgram $out/bin/racer --set RUST_SRC_PATH "${rustSrc}/src"
+    wrapProgram $out/bin/racer --set RUST_SRC_PATH "${rustc.src}/src"
   '';
 
   meta = with stdenv.lib; {
-    description = "A utility intended to provide rust code completion for editors and IDEs.";
+    description = "A utility intended to provide Rust code completion for editors and IDEs.";
     homepage = https://github.com/phildawes/racer;
     license = stdenv.lib.licenses.mit;
     maintainers = [ maintainers.jagajaga ];