Revert "[libc++][test] Mark ranges.transform.pass.cpp UNSUPPORTED for AIX"

[jloser]

Summary

This reverts commit 3583826bb52a7f129b55df043e29860aeab9906d.

Instead of marking the test unsupported for AIX, the choice is to bump the
timeout for CI as done in 76c7e1f2a8820b057de1a241422294bf25fdea2d and
222bd83d505728fca2bbe16cef8b93c321dd8c13

libcxx/test/std/algorithms/alg.modifying.operations/alg.transform/ranges.transform.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++03, c++11, c++14, c++17
 // UNSUPPORTED: libcpp-has-no-incomplete-ranges
-// On AIX the test takes a long time, leading to frequent CI timeouts.
-// UNSUPPORTED: LIBCXX-AIX-FIXME
 
 // <algorithm>
 
 // template<input_iterator I, sentinel_for<I> S, weakly_incrementable O,
 //          copy_constructible F, class Proj = identity>
 //   requires indirectly_writable<O, indirect_result_t<F&, projected<I, Proj>>>
 //   constexpr ranges::unary_transform_result<I, O>
 //     ranges::transform(I first1, S last1, O result, F op, Proj proj = {});