Delete 2.5.nix

delete orphan file

```gradle_2_5``` is in ```default.nix```

pkgs/development/tools/build-managers/gradle/2.5.nix

@@ -1,39 +0,0 @@
-{ stdenv, fetchurl, unzip, jdk, makeWrapper }:
-
-stdenv.mkDerivation rec {
-  name = "gradle-2.5";
-
-  src = fetchurl {
-    url = "http://services.gradle.org/distributions/${name}-bin.zip";
-    sha256 = "0mc5lf6phkncx77r0papzmfvyiqm0y26x50ipvmzkcsbn463x59z";
-  };
-
-  installPhase = ''
-    mkdir -pv $out/gradle
-    cp -rv lib $out/gradle
-
-    gradle_launcher_jar=$(echo $out/gradle/lib/gradle-launcher-*.jar)
-    test -f $gradle_launcher_jar
-    makeWrapper ${jdk}/bin/java $out/bin/gradle \
-      --set JAVA_HOME ${jdk} \
-      --add-flags "-classpath $gradle_launcher_jar org.gradle.launcher.GradleMain"
-  '';
-
-  phases = "unpackPhase installPhase";
-
-  buildInputs = [ unzip jdk makeWrapper ];
-
-  meta = {
-    description = "Enterprise-grade build system";
-    longDescription = ''
-      Gradle is a build system which offers you ease, power and freedom.
-      You can choose the balance for yourself. It has powerful multi-project
-      build support. It has a layer on top of Ivy that provides a 
-      build-by-convention integration for Ivy. It gives you always the choice
-      between the flexibility of Ant and the convenience of a 
-      build-by-convention behavior.
-    '';
-    homepage = http://www.gradle.org/;
-    license = stdenv.lib.licenses.asl20;
-  };
-}