Remove obsolete default-FOO variables

Remove obsolete default-FOO variables

* etc/NEWS: Indicate the removed variables.
* lisp/emacs-lisp/edebug.el (edebug-outside-mark): Fix comment.
* lisp/subr.el (default-mode-line-format, default-header-line-format):
(default-line-spacing, default-abbrev-mode, default-ctl-arrow):
(default-truncate-lines, default-left-margin, default-tab-width):
(default-case-fold-search, default-left-margin-width):
(default-right-margin-width, default-left-fringe-width):
(default-right-fringe-width, default-fringes-outside-margins):
(default-scroll-bar-width, default-vertical-scroll-bar):
(default-indicate-empty-lines, default-indicate-buffer-boundaries):
(default-fringe-indicator-alist, default-fringe-cursor-alist):
(default-scroll-up-aggressively, default-scroll-down-aggressively):
(default-fill-column, default-cursor-type):
(default-cursor-in-non-selected-windows):
(default-buffer-file-coding-system, default-major-mode):
(default-enable-multibyte-characters): Remove obsolete declarations.
* src/buffer.c (default-mode-line-format, default-header-line-format):
(default-line-spacing, default-abbrev-mode, default-ctl-arrow):
(default-truncate-lines, default-left-margin, default-tab-width):
(default-case-fold-search, default-left-margin-width):
(default-right-margin-width, default-left-fringe-width):
(default-right-fringe-width, default-fringes-outside-margins):
(default-scroll-bar-width, default-vertical-scroll-bar):
(default-indicate-empty-lines, default-indicate-buffer-boundaries):
(default-fringe-indicator-alist, default-fringe-cursor-alist):
(default-scroll-up-aggressively, default-scroll-down-aggressively):
(default-fill-column, default-cursor-type):
(default-cursor-in-non-selected-windows):
(default-buffer-file-coding-system, default-major-mode):
(default-enable-multibyte-characters): Remove.
* src/fileio.c (choose_write_coding_system): Fix comment.
* src/lisp.h (DEFVAR_BUFFER_DEFAULTS): Remove.