bpo-43892: Make match patterns explicit in the AST (GH-25585)

Co-authored-by: Brandt Bucher <brandtbucher@gmail.com>

Include/internal/pycore_symtable.h

@@ -32,7 +32,6 @@ struct symtable {
                                        the symbol table */
     int recursion_depth;            /* current recursion depth */
     int recursion_limit;            /* recursion limit */
-    int in_pattern;                 /* whether we are currently in a pattern */
 };
 
 typedef struct _symtable_entry {