patch 8.2.0114: info about sourced scripts is scattered

Problem:    Info about sourced scripts is scattered.
Solution:   Use scriptitem_T for info about a script, including s: variables.
            Drop ga_scripts.

src/eval.c

@@ -149,8 +149,7 @@ eval_init(void)
 eval_clear(void)
 {
     evalvars_clear();
-
-    free_scriptnames();
+    free_scriptnames();  // must come after evalvars_clear().
     free_locales();
 
     // autoloaded script names