[libc++] Simplify std::function further after removing allocator support

[philnik777]

Since we've removed allocator support, we can remove a few support structures. This only affects the policy implementation, so this shouldn't even be ABI sensitive.

[github-actions]

⚠️ C/C++ code formatter, clang-format found issues in your code. ⚠️

You can test this locally with the following command:

git-clang-format --diff HEAD~1 HEAD --extensions h -- libcxx/include/__functional/function.h

View the diff from clang-format here.

diff --git a/libcxx/include/__functional/function.h b/libcxx/include/__functional/function.h
index f0c00c56c..dc112ebfd 100644
--- a/libcxx/include/__functional/function.h
+++ b/libcxx/include/__functional/function.h
@@ -456,7 +456,7 @@ public:
   template <class _Fp, __enable_if_t<!is_same<__decay_t<_Fp>, __policy_func>::value, int> = 0>
   _LIBCPP_HIDE_FROM_ABI explicit __policy_func(_Fp&& __f) : __policy_(__policy::__create_empty()) {
     if (__function::__not_null(__f)) {
-      __func_ = __call_func<_Fp>;
+      __func_   = __call_func<_Fp>;
       __policy_ = __policy::__create<_Fp>();
       if (__use_small_storage<_Fp>()) {
         ::new ((void*)&__buf_.__small) _Fp(std::move(__f));