Revert "bootloader: grub: Add gfxmode (resolution) override."

This reverts commit a23091880d.
It causes ‘guix pull’ to fail: <https://paste.debian.net/plain/1125061>.

doc/guix.texi

@@ -25923,22 +25923,9 @@ must @emph{not} be an OS device name such as @file{/dev/sda1}.
 @end table
 @end deftp
 
-@cindex HDPI
-@cindex HiDPI
-@cindex resolution
 @c FIXME: Write documentation once it's stable.
-For now only GRUB has theme support.  GRUB themes are created using
+For now only GRUB has theme support. GRUB themes are created using
-the @code{grub-theme} form, which is not fully documented yet.
+the @code{grub-theme} form, which is not documented yet.
-
-@deftp {Data Type} grub-theme
-Data type representing the configuration of the GRUB theme.
-
-@table @asis
-@item @code{gfxmode} (default: @code{'("auto")})
-The GRUB @code{gfxmode} to set (a list of screen resolution strings, see
-@pxref{gfxmode,,, grub, GNU GRUB manual}).
-@end table
-@end deftp
 
 @defvr {Scheme Variable} %default-theme
 This is the default GRUB theme used by the operating system if no
@@ -25949,17 +25936,6 @@ It comes with a fancy background image displaying the GNU and Guix
 logos.
 @end defvr
 
-For example, to override the default resolution, you may use something
-like
-
-@lisp
-(bootloader
- (grub-configuration
- ;; @dots{}
- (theme (grub-theme
-         (inherit %default-theme)
-         (gfxmode '("1024x786x32" "auto"))))))
-@end lisp
 
 @node Invoking guix system
 @section Invoking @code{guix system}

gnu/bootloader/grub.scm

@@ -3,7 +3,6 @@
 ;;; Copyright © 2016 Chris Marusich <cmmarusich@gmail.com>
 ;;; Copyright © 2017 Leo Famulari <leo@famulari.name>
 ;;; Copyright © 2017 Mathieu Othacehe <m.othacehe@gmail.com>
-;;; Copyright © 2019 Jan (janneke) Nieuwenhuizen <janneke@gnu.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -89,9 +88,7 @@ (define-record-type* <grub-theme>
   (color-normal    grub-theme-color-normal
                    (default '((fg . cyan) (bg . blue))))
   (color-highlight grub-theme-color-highlight
-                   (default '((fg . white) (bg . blue))))
+                   (default '((fg . white) (bg . blue)))))
-  (gfxmode         grub-gfxmode
-                   (default '("auto"))))          ;list of string
 
 (define %background-image
   (grub-image
@@ -152,10 +149,8 @@ (define setup-gfxterm-body
     ;; most other modern architectures have no other mode and therefore don't
     ;; need to be switched.
     (if (string-match "^(x86_64|i[3-6]86)-" system)
-        (string-append "
+        "
-  set gfxmode=" (string-join
+  # Leave 'gfxmode' to 'auto'.
-                 (grub-gfxmode (bootloader-configuration-theme config))
-                 ";") "
   insmod video_bochs
   insmod video_cirrus
   insmod gfxterm
@@ -171,7 +166,7 @@ (define setup-gfxterm-body
     insmod vbe
     insmod vga
   fi
-")
+"
         ""))
 
   (define (setup-gfxterm config font-file)