Fix external packages built on drdr.
Remove release announcements.

These are now in the `racket/racket-lang-org` repository.
Split `meta/images/taking-screenshots` from the repository.

This is now in the `racket/taking-screenshots` repository.
Remove `mkheart.rkt`, which has been moved to the `racket/drracket`
repository.
Move unix installer test to the "racket-test" pkg.
Now that this isn't an actual package, it doesn't need metadata.
raco pkg update: make update to non-clone suggest more non-clone conversions

In other words, suggestion conversions in the non-clone direction the
same as conversions in the clone direction. As a way of disambiguation
the right direction, the non-clone direction is only suggested for
sharing that is immediately discovered from the command-line arguments
(as opposed to sharing that becomes apparent as other packages are
updated or installed via dependencies).
raco pkg: change default answer on clone-sharing conversion to "Y"
raco pkg update: allow `--update-deps` with a linked package

The linked package cannot be updated, but maybe its dependencies
can, so just alert the user that the linked package is skipped
instead of rejecting the request.
raco pkg: fix path problems with updating a clone-linked package
raco pkg update: recognize a directory that coresponds to a clone link

For example,

 raco pkg update --clone my/clone/test-pkg
 raco pkg update my/clone/test-pkg

will check for updates in the second case, not change the installation
to a directory link.
move unix-installer test to "distro-build-test"
adjust status reporting for `raco pkg update`

Reduce a little noise that was recently introduced.
pkg/dirs-catalog added

This utility that is needed by `make` turns out to be useful in other
scripts.
remove the "racket-pkgs" directory layer

The layer is now redundant, since everything left in "pkgs" is in the
"racket-pkgs" category.
fix handling of "links.rktd" errors
add makefile step to adjust for movements within "pkgs"

The step doesn't currently adapt to additionals or removals
from "pkgs", so further support may be needed in the future.
get-pkg-context: add `#:use-cache?` and `#:quiet?` arguments
doc clarification on `beg0` bytecode form

From Gustavo, and intended to be part of commit
2d95c39051.
pkg info.rkt: refine specification of `distribution-preference`