Fix some more contrib issues

* contrib/sly-fontifying-fu.el (sly-activate-font-lock-magic): Remove
xemacs branch.

* contrib/sly-mrepl.el (sly-mrepl--copy-objects-to-repl)
(sly-mrepl-sync-package-and-default-directory)
(sly-mrepl--insert-output): Simplify.

* lib/sly-buttons.el (sly-part-button-keymap): Don't bind RET
here.

* lib/lisp/backend/swank-allegro.lisp (frame-restartable-p):
Remove spurious and useless log.
Fixes to the "Copy Call to REPL" interface

* sly.el (sldb--guess-frame-name): New function.
(sldb-frame-button): Use it.

* contrib/sly-mrepl.el (define-sly-contrib sly-mrepl): Better keydindings.