chore: cleanup unused attributes for the host_toolchain repo rule (#2195)

The attributes were not used, so we can remove them for now.

examples/bzlmod/MODULE.bazel.lock

diff --git a/examples/bzlmod/MODULE.bazel.lock b/examples/bzlmod/MODULE.bazel.lock
index 6964e11..d747ed3 100644
--- a/examples/bzlmod/MODULE.bazel.lock
+++ b/examples/bzlmod/MODULE.bazel.lock
@@ -1231,7 +1231,7 @@
     },
     "@@rules_python~//python/extensions:pip.bzl%pip": {
       "general": {
-        "bzlTransitiveDigest": "ofS5ggL4YnyCZejN3Rimf+XXWMSwuWypjGghv3fbAGY=",
+        "bzlTransitiveDigest": "vzdh1M3LRVqyF10AVUO1+FOE7CZwlZaFT+7RgQ4OKXg=",
         "usagesDigest": "MChlcSw99EuW3K7OOoMcXQIdcJnEh6YmfyjJm+9mxIg=",
         "recordedFileInputs": {
           "@@other_module~//requirements_lock_3_11.txt": "a7d0061366569043d5efcf80e34a32c732679367cb3c831c4cdc606adc36d314",
@@ -6140,7 +6140,7 @@
     },
     "@@rules_python~//python/private/pypi:pip.bzl%pip_internal": {
       "general": {
-        "bzlTransitiveDigest": "LJJOkml9ZwY4i0WJnh+pN5fZUQLciL7hPL27L8kNYeI=",
+        "bzlTransitiveDigest": "TgRegkReKbGzK4VxYz9up697gcf5Q8NFuZYnZHryck8=",
         "usagesDigest": "Y8ihY+R57BAFhalrVLVdJFrpwlbsiKz9JPJ99ljF7HA=",
         "recordedFileInputs": {
           "@@rules_python~//tools/publish/requirements.txt": "031e35d03dde03ae6305fe4b3d1f58ad7bdad857379752deede0f93649991b8a",

python/private/python_repositories.bzl

diff --git a/python/private/python_repositories.bzl b/python/private/python_repositories.bzl
index 46b2e29..b65127b 100644
--- a/python/private/python_repositories.bzl
+++ b/python/private/python_repositories.bzl
@@ -692,12 +692,7 @@
                 platform = platform,
             ))
 
-    host_toolchain(
-        name = name + "_host",
-        python_version = python_version,
-        user_repository_name = name,
-        platforms = loaded_platforms,
-    )
+    host_toolchain(name = name + "_host")
 
     toolchain_aliases(
         name = name,

python/private/toolchains_repo.bzl

diff --git a/python/private/toolchains_repo.bzl b/python/private/toolchains_repo.bzl
index df16fb8..21c4e90 100644
--- a/python/private/toolchains_repo.bzl
+++ b/python/private/toolchains_repo.bzl
@@ -314,14 +314,6 @@
 this repo causes an eager fetch of the toolchain for the host platform.
     """,
     attrs = {
-        "platforms": attr.string_list(
-            doc = "List of platforms for which aliases shall be created",
-        ),
-        "python_version": attr.string(doc = "The Python version."),
-        "user_repository_name": attr.string(
-            mandatory = True,
-            doc = "The base name for all created repositories, like 'python38'.",
-        ),
         "_rule_name": attr.string(default = "host_toolchain"),
         "_rules_python_workspace": attr.label(default = Label("//:WORKSPACE")),
     },