doc,lib,src,test: strip executable bits off files

Remove the executable bits of the file modes of some files that
accidentally received it.

PR-URL: https://github.com/nodejs/node/pull/15132


Reviewed-By: Timothy Gu <timothygu99@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>