* INSTALL: Remove the "by hand" sections.
No-one needs to know those details, and this file is too long already.
* README: Remove some unnecessary detail.
Remove some admin/notes files

* admin/notes/lel-TODO: Remove.  This has not turned out to be a
useful way to get things documented.

* admin/notes/exit-value, admin/notes/iftc: Remove.
These don't seem to have any particular relationship to Emacs development.
* admin/notes/versioning: Relocate and rewrite.
* nextstep/README: Move most contents into INSTALL.
Remove license notice from file, since it is now trivial.