Remove deprecated cgo_genrules

vendor/github.com/coreos/pkg/dlopen/BUILD

@@ -4,25 +4,9 @@ licenses(["notice"])
 
 load(
     "@io_bazel_rules_go//go:def.bzl",
-    "cgo_genrule",
     "go_library",
 )
 
-cgo_genrule(
-    name = "cgo_codegen",
-    srcs = [
-        "dlopen.go",
-        "dlopen_example.go",
-    ],
-    clinkopts = [
-        "-lz",
-        "-lm",
-        "-lpthread",
-        "-ldl",
-    ],
-    tags = ["automanaged"],
-)
-
 go_library(
     name = "go_default_library",
     srcs = [