Remove copyright headers from source files

[archmoj]

The headers in the source files slightly complicated our development and build processes.
As discussed by @alexcjohnson

• to avoid several redundant headers endup in the bundles without the costly browserify transform added in Avoid redundant plotly.js copyright comments in bundles #5439
• to avoid test failures when new files are added without the header
• to avoid a big PR every new year, and making every other open PR update to pass tests at the same time, annoying and potentially conflict-inducing for community PRs

This PR simplies all that by removing the headers from the src and lib folders.
To do so I adjusted the script in ee1aca8 and use that to make the changes.

cc: #5395

@plotly/plotly_js

[alexcjohnson]

licenseSrc is still used in

plotly.js/tasks/sync_packages.js

Line 242 in ccdd29a

var cnt = [constants.licenseSrc, ''];

Is this desired? Looks like this is creating a file to be published so licenseDist may be more appropriate here?

[archmoj]

licenseSrc is still used in

plotly.js/tasks/sync_packages.js

Line 242 in ccdd29a

var cnt = [constants.licenseSrc, ''];

Is this desired? Looks like this is creating a file to be published so licenseDist may be more appropriate here?

Good call. Addressed in adbed4b.

[alexcjohnson]

💃 LGTM!