remove some obsolete files
setup/getinfo: add `#:bootstrap?' mode

Bootstrap mode disables the use of a compiled form of "info.rkt",
in case the compiled form is broken. It also attaches `info'-language
modules from the `setup/getinfo' namespace to the "info.rkt"-loading
namespace.

Formerly, `raco setup' relied on capturing the bytecode-compilation
bootstrap context used for `raco setup' itself when loading info
files. But when `raco pkg install' used `raco setup', it didn't have
the same bootstrapping context in place, so it could get confused
(e.g., if you unlink a package from one Racket version and install it
as a link in a different Racket version). Now, both `raco setup' and
`raco pkg' use `#:bootstrap?' mode for `get-info/full'.