Change each repository LICENSE file for compatibility to pkg.go.dev.

[zchee]

We might be better to change each repositoryLICENSE file to an actual license comment for compatibility to pkg.go.dev

The pkg.go.dev has a license policy, so if https://github.com/google/licensecheck can't parse the repository license file, pkg.go.dev didn't show any documentation.

See also:

• pkg.go.dev license policy
• https://pkg.go.dev/github.com/go-clang/clang-v3.9/clang
  • clang-v3.9 LICENSE file
• https://pkg.go.dev/github.com/go-clang/clang-v3.6/clang (temporary created for check Go module behaviour)
  • clang-v3.6 LICENSE file

[zchee]

/cc @sbinet

[zchee]

changed. Close.