Remove redundant @nixpkgs

The corresponding files no longer exist and the import was no longer in
effect since the @nixpkgs import in docs_dependencies_2 took precedence.

Author: aherrmann

WORKSPACE

@@ -24,16 +24,9 @@ docs_dependencies_2()
 load(
     "//nixpkgs:nixpkgs.bzl",
     "nixpkgs_git_repository",
-    "nixpkgs_local_repository",
     "nixpkgs_package",
 )
 
-nixpkgs_local_repository(
-    name = "nixpkgs",
-    nix_file = "@rules_nixpkgs_core//:nixpkgs.nix",
-    nix_file_deps = ["@rules_nixpkgs_core//:nixpkgs.json"],
-)
-
 nixpkgs_package(
     name = "nix_2_10",
     attribute_path = "nixVersions.nix_2_10",