Check SteamDeck in keyboard_is_available

desktop_version/src/ButtonGlyphs.cpp

@@ -152,7 +152,7 @@ bool BUTTONGLYPHS_keyboard_is_available(void)
 {
     /* Returns true if it makes sense to show button hints that are only available
      * on keyboards (like press M to mute), false if we're on a console. */
-    return true;
+    return !SDL_GetHintBoolean("SteamDeck", SDL_FALSE);
 }
 
 bool BUTTONGLYPHS_keyboard_is_active(void)