Remove header licenses across the project

[Mark-Simulacrum]

This pull request removes the header licenses from files across the Rust repository.

I've attempted to check for any remaining headers and removed all of them -- any we've missed can be removed in the future; there's nothing blocking that.

Unfortunately, not all of the changes are as basic as "removing a header" because some of them required test file updates or otherwise. However, I am fairly confident that the changes in this pull request, while wide-sweeping, are unlikely to actually make any tests fail to properly test the code; any non-script based changes were manual and carefully verified.

r? @pietroalbini cc @rust-lang/infra

[emilyalbini]

@bors r+ p=1000

It would be nice to get a tidy check that looks for the header in the future, but that doesn't need to be included in this PR. Thanks Mark! 🎉

[bors]

📌 Commit d147ce5ae307dd04541fa603daeed15ffce27462 has been approved by pietroalbini

[bors]

⌛ Testing commit d147ce5ae307dd04541fa603daeed15ffce27462 with merge 9e35dc0e3aee786a3b439828ed40374c8af8259c...

[bors]

💔 Test failed - status-appveyor

[Mark-Simulacrum]

@bors r=pietroalbini

[bors]

📌 Commit d797cd6e258ff1b24039992c92d9df03a2e762d6 has been approved by pietroalbini

[bors]

⌛ Testing commit d797cd6e258ff1b24039992c92d9df03a2e762d6 with merge 8b53008d9ee36cfb8ebdb9a1af3377c026bbcd06...

[bors]

💔 Test failed - status-travis

[Mark-Simulacrum]

Could've sworn I had tested these test failures...

@bors r=pietroalbini

[emilyalbini]

@bors treeclose-

[sanmai-NL]

@Mark-Simulacrum What was the motivation for this change? How does it bear on e.g. #25664?

[Mark-Simulacrum]

No bearing, to my knowledge. The code is still licensed as before (MIT/Apache), just is cleaner by skipping the ~10 lines of boilerplate code in every file.

[sanmai-NL]

@Mark-Simulacrum: I agree about it looking cleaner. But I remember past discussion on GitHub where, if I recall correctly, Mozilla was said to have found the license header at the top of every source file legally necessary.

What do you think about adding SPDX comments to every file instead? See https://spdx.org/sites/cpstandard/files/pages/files/using_spdx_license_list_short_identifiers.pdf . Within a project of mine, this was required.

[Mark-Simulacrum]

If you'd like to discuss this further, let's do it on internals (this isn't the best place).

However, I believe that the current decision will stand unless there's some firm evidence to do otherwise; see #53654, #53617, and #43498 for the primary discussion.

[SimonSapin]

@Mark-Simulacrum, @pietroalbini, was there previous discussion of this change somewhere? Not that I’m opposed to it, but I’m curious of the arguments. Do the reasons these headers were added in the first place no longer hold? Why?

[emilyalbini]

@SimonSapin the discussion was in #43498.

[Mark-Simulacrum]

See #53654, #53617, and #43498 - the core team discussed this a while back and came to the conclusion that the header is no longer necessary.