runtime: drop deprecated Ctrl-key constant names

tcell v3 removes the legacy KeyCtrlSpace / KeyCtrlLeftSq /
KeyCtrlBackslash / KeyCtrlRightSq / KeyCtrlCarat / KeyCtrlUnderscore
constants. Micro's bindings parser previously accepted the matching
string names ("CtrlSpace", "CtrlLeftSq", ...) as aliases; those are
now invalid and the parser emits a TermMessage warning when it sees
one.

Update the shipped comment plugin and the keybindings help page to
use the supported forms.

Assisted-by: Claude:claude-opus-4-7

Author: Tubbles

runtime/help/keybindings.md

@@ -452,7 +452,6 @@ F61
 F62
 F63
 F64
-CtrlSpace
 Ctrl-a
 Ctrl-b
 Ctrl-c
@@ -479,11 +478,6 @@ Ctrl-w
 Ctrl-x
 Ctrl-y
 Ctrl-z
-CtrlLeftSq
-CtrlBackslash
-CtrlRightSq
-CtrlCarat
-CtrlUnderscore
 Backspace
 OldBackspace
 Tab

runtime/plugins/comment/comment.lua

@@ -217,6 +217,6 @@ end
 function init()
     config.MakeCommand("comment", comment, config.NoComplete)
     config.TryBindKey("Alt-/", "lua:comment.comment", false)
-    config.TryBindKey("CtrlUnderscore", "lua:comment.comment", false)
+    config.TryBindKey("Ctrl-_", "lua:comment.comment", false)
     config.AddRuntimeFile("comment", config.RTHelp, "help/comment.md")
 end

runtime/plugins/comment/help/comment.md

@@ -2,8 +2,8 @@
 
 The comment plugin provides auto commenting/uncommenting.
 The default binding to comment/uncomment a line is `Alt-/`
-and `CtrlUnderscore`, which is equivalent in most terminals
-to `Ctrl-/`. You can easily modify that in your `bindings.json`
+and `Ctrl-_`, which is equivalent in most terminals to
+`Ctrl-/`. You can easily modify that in your `bindings.json`
 file:
 
 ```json