Don't bind a hotkey for Fire Guardian summoning

The action of binding a hotkey persists during the same game session,
and in this particular case since we're reusing a hotkey that's already
bound to an engine command, some dumb behaviour ensues when switching to
a scenario where the menu item doesn't exist and the player needs to use
the engine command again.

This bug was 7 years old.

changelog.md

@@ -19,6 +19,9 @@ Version 0.10.5+dev:
       affecting a lore glyph.
   * E3S8C - Breakdown:
     * Increase turn limit.
+    * Don't bind a hotkey for the Summon Fire Guardian menu item since it gives
+      the game engine an existential crisis when switching scenarios in the
+      same session.
 
 * Units:
   * Enable Troll Whelp → Troll Shaman unit progression for new runs.

macros/unit-utils.cfg

@@ -575,14 +575,6 @@
         # po: wesnoth-units textdomain in mainline.
         description= _ "Summon Fire Guardian"
         image="icons/menu-fire.png"
-        [default_hotkey]
-            key=r
-#ifdef APPLE
-            cmd=yes
-#else
-            ctrl=yes
-#endif
-        [/default_hotkey]
         [show_if]
             # Only during the player's turn
             {VARIABLE_NUMERICAL_EQUALS side_number 1}