Remove atheris (#14212)

Closes: #14185

stubs/atheris/METADATA.toml

@@ -1,11 +0,0 @@
-version = "2.3.*"
-upstream_repository = "https://github.com/google/atheris"
-partial_stub = true
-no_longer_updated = true
-
-[tool.stubtest]
-ignore_missing_stub = true
-# TODO (2025-03-05): unskip once `atheris` can be installed on `ubuntu-24.04`,
-# see https://github.com/python/typeshed/pull/13582 and
-# https://github.com/google/atheris/issues/82
-skip = true