Retire legacy grid web shell (#535)

* Retire unused legacy web shell.

* Remove legacy shell references in Xgi, backends and menu.

* Address leftover (w)shell occurrences in templates and fixtures as pointed out
in review (Thanks @Martin-Rehr).

* Remove leftover `shell.css`, too, as suggested in review (Thanks @Martin-Rehr).

Author: jonasbardino

mig/cgi-bin/shell.py

@@ -4,7 +4,7 @@
 # --- BEGIN_HEADER ---
 #
 # bluesky - alternative style for all pages
-# Copyright (C) 2003-2014  The MiG Project lead by Brian Vinter
+# Copyright (C) 2003-2026  The MiG Project by the Science HPC Center at UCPH
 #
 # This file is part of MiG.
 #
@@ -98,7 +98,7 @@ div.container {
   /* No footer overlap with menu here */
   min-height: 0px;
 }
-/* override block layout for maximized areas like wshell */
+/* override block layout for maximized areas without menu */
 #nomenu {
   margin: 4px;
 }
@@ -158,9 +158,6 @@ div.container {
 .navmenu ul li.settings a {
   background-image: url('/images/icons/wrench.png');
 }
-.navmenu ul li.shell a {
-  background-image: url('/images/icons/application_osx_terminal.png');
-}
 .navmenu ul li.people a {
   background-image: url('/images/icons/personal.png');
 }

mig/images/bluesky.css

@@ -4,7 +4,7 @@
 # --- BEGIN_HEADER ---
 #
 # default - default style settings for all pages
-# Copyright (C) 2003-2021  The MiG Project lead by Brian Vinter
+# Copyright (C) 2003-2026  The MiG Project by the Science HPC Center at UCPH
 #
 # This file is part of MiG.
 #
@@ -339,7 +339,7 @@ table.peers {
   min-height: 500px;
 }
 
-/* override block layout for maximized areas like wshell */
+/* override block layout for maximized areas without menu */
 .nomenu #content, .nomenu .contentblock {
   margin: 4px;
 }
@@ -436,9 +436,6 @@ table.peers {
 .navmenu ul li.settings a, #legacy-ui-body .app-grid .fas.settings {
   background-image: url('/images/icons/user.png');
 }
-.navmenu ul li.shell a, #legacy-ui-body .app-grid .fas.shell {
-  background-image: url('/images/icons/application_osx_terminal.png');
-}
 .navmenu ul li.people a, #legacy-ui-body .app-grid .fas.people {
   background-image: url('/images/icons/group.png');
 }