cleanup: remove unused sanitize_platform_name function (#2887)

The sanitize_platform_name function is unused, so remove it.

python/private/toolchains_repo.bzl

diff --git a/python/private/toolchains_repo.bzl b/python/private/toolchains_repo.bzl
index d0814b6..7557c9f 100644
--- a/python/private/toolchains_repo.bzl
+++ b/python/private/toolchains_repo.bzl
@@ -404,9 +404,6 @@
     },
 )
 
-def sanitize_platform_name(platform):
-    return platform.replace("-", "_")
-
 def _get_host_platform(*, rctx, logger, python_version, os_name, cpu_name, platforms):
     """Gets the host platform.