Remove upb gencode from upb/cmake/

This code appears to be unused, and is also duplicated in upb/reflection/cmake
and upb/reflection/stage0.

PiperOrigin-RevId: 728772596

Author: acozzette

regenerate_stale_files.sh

@@ -23,7 +23,6 @@ STALENESS_TESTS=(
   "php:test_amalgamation_staleness"
   "php:proto_staleness_test"
   "ruby/ext/google/protobuf_c:test_amalgamation_staleness"
-  "upb/cmake:test_generated_files"
   "upb/reflection:descriptor_upb_proto_staleness_test"
   "upb_generator:plugin_upb_proto_staleness_test"
 )

upb/cmake/BUILD.bazel

@@ -6,10 +6,6 @@
 # https://developers.google.com/open-source/licenses/bsd
 
 load("@rules_pkg//pkg:mappings.bzl", "pkg_files", "strip_prefix")
-load(
-    ":build_defs.bzl",
-    "staleness_test",
-)
 
 licenses(["notice"])
 
@@ -38,17 +34,6 @@ genrule(
     cmd = "cp $(SRCS) $(@D)/generated-in/google/protobuf",
 )
 
-staleness_test(
-    name = "test_generated_files",
-    outs = [
-        "google/protobuf/descriptor.upb.h",
-        "google/protobuf/descriptor.upb_minitable.c",
-        "google/protobuf/descriptor.upb_minitable.h",
-    ],
-    generated_pattern = "generated-in/%s",
-    tags = ["manual"],
-)
-
 pkg_files(
     name = "upb_cmake_dist",
     srcs = [