* lisp/emacs-lisp/backtrace.el (backtrace-mode-map): Update
bindings and menu items with new function names.
(backtrace-collapse, backtrace-pretty-print)
(backtrace--collapse, backtrace--pretty-print): Remove functions.
(backtrace-single-line, backtrace-multi-line)
(backtrace--single-line, backtrace--multi-line): New functions.
(backtrace--reformat-sexp): Remove 'error-message' argument.
* test/lisp/emacs-lisp/backtrace-tests.el
(backtrace-tests--pretty-print-and-collapse): Remove.
(backtrace-tests--single-and-multi-line): New test.
(backtrace-tests--verify-pp-and-collapse): Remove.
(backtrace-tests--verify-single-and-multi-line): New function.