libssh2_1_10: remove temp attr

it was added in https://github.com/NixOS/nixpkgs/commit/28b6a910

pkgs/development/libraries/libssh2/1_10.nix

@@ -1,10 +0,0 @@
-{ libssh2, fetchurl }:
-
-libssh2.overrideAttrs (attrs: rec {
-  version = "1.10.0";
-  src = fetchurl {
-    url = with attrs; "${meta.homepage}/download/${pname}-${version}.tar.gz";
-    sha256 = "sha256-LWTpDz3tOUuR06LndMogOkF59prr7gMAPlpvpiHkHVE=";
-  };
-  patches = [];
-})

pkgs/top-level/all-packages.nix

@@ -19134,8 +19134,6 @@ with pkgs;
   libssh = callPackage ../development/libraries/libssh { };
 
   libssh2 = callPackage ../development/libraries/libssh2 { };
-  #FIXME: temporary attribute
-  libssh2_1_10 = callPackage ../development/libraries/libssh2/1_10.nix { };
 
   libstartup_notification = callPackage ../development/libraries/startup-notification { };