[runtimes][NFC] Remove filenames at the top of the license notice

We've stopped doing it in libc++ for a while now because these names
would end up rotting as we move things around and copy/paste stuff.
This cleans up all the existing files so as to stop the spreading
as people copy-paste headers around.

GitOrigin-RevId: eb8650a75793b2bd079d0c8901ff066f129061da
81 files changed