Remove explicit py_* loads (#781)

Per https://groups.google.com/g/bazel-discuss/c/XNvpWcge4AE/m/aJ-aQzszAwAJ

github_tools/BUILD

@@ -2,7 +2,6 @@
 # Exceptions. See /LICENSE for license information.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-load("@rules_python//python:defs.bzl", "py_binary", "py_library", "py_test")
 load("@py_deps//:requirements.bzl", "requirement")
 load("@mypy_integration//:mypy.bzl", "mypy_test")
 

migrate_cpp/BUILD

@@ -2,7 +2,6 @@
 # Exceptions. See /LICENSE for license information.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-load("@rules_python//python:defs.bzl", "py_binary")
 load("@mypy_integration//:mypy.bzl", "mypy_test")
 
 py_binary(

proposals/scripts/BUILD

@@ -2,7 +2,6 @@
 # Exceptions. See /LICENSE for license information.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-load("@rules_python//python:defs.bzl", "py_binary", "py_library", "py_test")
 load("@mypy_integration//:mypy.bzl", "mypy_test")
 
 py_library(