Simplify osascript handling

This makes a few changes, somewhat independent, but all related:
* defaults `auto-dark-allow-osascript` to true[^1];
* falls back to `osascript` on-demand if neither `ns-do-applescript` nor
  `mac-do-applescript` is available[^2]; and
* removes `osascript` as a separate `auto-dark-detection-method`[^3].

These can be easily separated depending on which, if any, you think are
improvements.

[^1]: I don’t know why this is even a variable. If it’s not allowed, then there
is no way to use Auto-Dark on systems that require it, and the failure mode is
opaque (“Could not determine a viable theme detection mechanism!”).

[^2]: If this change isn’t made, then the error message “Try setting
`auto-dark-allow-osascript` to t” doesn’t make sense, as it’s only reported in a
location where the value of `auto-dark-allow-osascript` has no effect. The
alternative is to change the error message to something like
“`auto-dark-detection-method` indicates that this Emacs build has AppleScript
support, but none could be found. Either rebuild Emacs with AppleScript support
or change the detection method and set `auto-dark-allow-osascript`”.

[^3]: With LionyxML#59, the two `fboundp` checks added before falling back to
`osascript` should be more than outweighed by the removal of shell invocation.

auto-dark.el

@@ -53,7 +53,7 @@ Emacs must be restarted for this value to take effect."
   :group 'auto-dark
   :type 'integer)
 
-(defcustom auto-dark-allow-osascript nil
+(defcustom auto-dark-allow-osascript t
   "Whether to allow function `auto-dark-mode' to shell out to osascript:
 to check dark-mode state, if `ns-do-applescript' or `mac-do-applescript'
 is not available."
@@ -74,7 +74,7 @@ if left as such.  Only change this value if you know what you're
 doing!"
   :group 'auto-dark
   :type 'symbol
-  :options '(applescript osascript dbus powershell winreg termux))
+  :options '(applescript dbus powershell winreg termux))
 
 (defvar auto-dark--last-dark-mode-state 'unknown)
 
@@ -87,7 +87,9 @@ In order to check if dark mode is enabled.  Return true if it is."
       (auto-dark--is-dark-mode-ns)
     (if (fboundp 'mac-do-applescript)
         (auto-dark--is-dark-mode-mac)
-      (error "No AppleScript support available in this Emacs build.  Try setting `auto-dark-allow-osascript` to t"))))
+      (if auto-dark-allow-osascript
+          (auto-dark--is-dark-mode-osascript)
+        (error "No AppleScript support available in this Emacs build.  Try setting `auto-dark-allow-osascript` to t")))))
 
 (defun auto-dark--is-dark-mode-ns ()
   "Check if dark mode is enabled using ns-do-applescript."
@@ -159,8 +161,6 @@ In order to determine if dark theme is enabled."
   (pcase auto-dark-detection-method
     ('applescript
      (auto-dark--is-dark-mode-applescript))
-    ('osascript
-     (auto-dark--is-dark-mode-osascript))
     ('dbus
      (auto-dark--is-dark-mode-dbus))
     ('powershell
@@ -272,15 +272,8 @@ Remove theme change callback registered with D-Bus."
 (defun auto-dark--determine-detection-method ()
   "Determine which theme detection method auto-dark should use."
   (cond
-   ((and (eq system-type 'darwin)
-         (or (fboundp 'ns-do-applescript)
-             (fboundp 'mac-do-applescript))
-		 (or (eq window-system 'ns)
-			 (eq window-system 'mac)))
+   ((eq system-type 'darwin)
     'applescript)
-   ((and (eq system-type 'darwin)
-         auto-dark-allow-osascript)
-    'osascript)
    ((and (eq system-type 'gnu/linux)
          (member 'dbus features)
          (member "org.freedesktop.portal.Desktop"