Remove C++11 style factory function in absl::Cleanup

[CJ-Johnson]

Since the release of absl::Cleanup, an upgrade tool has been available:

• Documentation: https://github.com/llvm/llvm-project/blob/main/clang-tools-extra/docs/clang-tidy/checks/abseil/cleanup-ctad.rst
• Implementation: https://github.com/llvm/llvm-project/blob/main/clang-tools-extra/clang-tidy/abseil/CleanupCtadCheck.cpp
• Tests: https://github.com/llvm/llvm-project/blob/main/clang-tools-extra/test/clang-tidy/checkers/abseil/cleanup-ctad.cpp

Now that Abseil requires C++17 or newer, this PR removes the old spelling, absl::MakeCleanup.

This PR might not be accepted, per the "API Freeze Consequences" mentioned at https://github.com/abseil/abseil-cpp/blob/master/CONTRIBUTING.md

I wanted to propose it to see if there was any interest in removal. And while here, I made some additional changes.

[derekmauro]

Hi CJ,

We haven't run the CTAD cleanup on the codebase, so there is no way we can consider deleting MakeCleanup() anytime soon.

In addition, pull requests should be focused on a single thing. Deleting a function should be isolated from unrelated changes. I did not look at the other changes. If you feel they are worth it, please say why.