gflags: alias to google-gflags

Both packages referred to the same repo (`gflags/gflags` at GitHub),
both packages used almost the same version (2.2.1 and 2.2.0). Therefore
I think that it's just fair to drop one of the packages to avoid
duplication and reduce the maintenance overload.

I decided to drop `gflags` originally packaged by @shlevy as it didn't
contain testing support as `google-gflags` does. The package set refers
from `gflags` to `google-gflags`, so both package names remain (to avoid
any confusions), however the `gflags` expression is removed.

pkgs/development/libraries/gflags/default.nix

@@ -1,19 +0,0 @@
-{ stdenv, fetchurl, cmake }:
-
-stdenv.mkDerivation
-  { name = "gflags-2.2.1";
-    src = fetchurl
-      { url = "https://github.com/gflags/gflags/archive/v2.2.1.tar.gz";
-        sha256 = "03lxc2ah8i392kh1naq99iip34k4fpv22kwflyx3byd2ssycs9xf";
-      };
-    nativeBuildInputs = [ cmake ];
-    # for case-insensitive filesystems
-    prePatch = "mv BUILD BUILD.bazel";
-
-    meta = with stdenv.lib; {
-      description = "C++ library that implements commandline flags processing";
-      homepage = "https://github.com/gflags/gflags";
-      license = licenses.bsd3;
-      platforms = platforms.unix;
-    };
-  }

pkgs/development/libraries/google-gflags/default.nix

@@ -2,13 +2,13 @@
 
 stdenv.mkDerivation rec {
   name = "google-gflags-${version}";
-  version = "2.2.0";
+  version = "2.2.1";
 
   src = fetchFromGitHub {
     owner = "gflags";
     repo = "gflags";
     rev = "v${version}";
-    sha256 = "1y5808ky8qhjwv1nf134czz0h2p2faqvjhxa9zxf8mg8hn4ns9wp";
+    sha256 = "12wkihc4f07qmhyqk3cjylj8v5xz2bjrq75p7aq1vvvj60fbp58k";
   };
 
   nativeBuildInputs = [ cmake ];

pkgs/top-level/all-packages.nix

@@ -8921,7 +8921,7 @@ with pkgs;
 
   gettext = callPackage ../development/libraries/gettext { };
 
-  gflags = callPackage ../development/libraries/gflags { };
+  gflags = google-gflags;
 
   gf2x = callPackage ../development/libraries/gf2x {};