boost175: drop

Obsolete version with no remaining users in the tree. Already removed
by other distributions.

pkgs/development/libraries/boost/1.75.nix

@@ -1,15 +0,0 @@
-{ callPackage, fetchurl, ... } @ args:
-
-callPackage ./generic.nix (args // rec {
-  version = "1.75.0";
-
-  src = fetchurl {
-    urls = [
-      "mirror://sourceforge/boost/boost_${builtins.replaceStrings ["."] ["_"] version}.tar.bz2"
-      "https://boostorg.jfrog.io/artifactory/main/release/${version}/source/boost_${builtins.replaceStrings ["."] ["_"] version}.tar.bz2"
-    ];
-    # SHA256 from http://www.boost.org/users/history/version_1_75_0.html
-    sha256 = "953db31e016db7bb207f11432bef7df100516eeb746843fa0486a222e3fd49cb";
-  };
-})
-

pkgs/development/libraries/boost/default.nix

@@ -16,7 +16,6 @@ let
       }
     );
 in {
-  boost175 = makeBoost ./1.75.nix;
   boost177 = makeBoost ./1.77.nix;
   boost178 = makeBoost ./1.78.nix;
   boost179 = makeBoost ./1.79.nix;