Reduce active message-log-max; scale in debug mode

8kb of log isn't really necessary. We'll scale it up when debug mode is
on, instead.

core/autoload/debug.el

@@ -12,7 +12,8 @@
     init-file-debug
     jka-compr-verbose
     url-debug
-    use-package-verbose)
+    use-package-verbose
+    (message-log-max . 16384))
   "A list of variable to toggle on `doom-debug-mode'.
 
 Each entry can be a variable symbol or a cons cell whose CAR is the variable