(Android) Do not show 'Quit RetroArch' by default

Android's navigation model expects the user to leave via Home or the task
switcher rather than an in-app control, and Google's Android TV
guidelines state outright that an exit item should not be shown in the
menu. There is no equivalent Play Store policy line for phones and
tablets, but the guidance points the same way and iOS is already
excluded from this entry in menu_displaylist.c.

Default menu_show_quit_retroarch to false on Android rather than
compiling the entry out, so the toggle remains available under
Settings -> User Interface -> Menu Item Visibility and existing configs
that already write the key are unaffected.

This depends on the preceding commit: until config is flushed on
APP_CMD_PAUSE, 'Quit RetroArch' is the only code path on Android that
saves the config at all, and hiding it by default would otherwise make
settings unsaveable.

config.def.h

@@ -828,7 +828,18 @@
 #define DEFAULT_MENU_SHOW_INFORMATION true
 #define DEFAULT_MENU_SHOW_CONFIGURATIONS true
 #define DEFAULT_MENU_SHOW_HELP true
+#if defined(ANDROID)
+/* Android's navigation model expects the user to leave via Home or the
+ * task switcher rather than an in-app control, and the Android TV
+ * guidelines state outright that an exit item should not appear in the
+ * menu. Default the entry off; the toggle stays available under
+ * Settings -> User Interface -> Menu Item Visibility for anyone who
+ * wants it back, and existing configs that already set the key are
+ * left untouched. */
+#define DEFAULT_MENU_SHOW_QUIT false
+#else
 #define DEFAULT_MENU_SHOW_QUIT true
+#endif
 #define DEFAULT_MENU_SHOW_RESTART true
 #define DEFAULT_MENU_SHOW_REBOOT true
 #define DEFAULT_MENU_SHOW_SHUTDOWN true