Make check_usermap() parameter names consistent.

The function has a bool argument named "case_insensitive", but that was
spelled "case_sensitive" in the declaration.  Make them consistent now
to avoid confusion in the future.

Author: Peter Geoghegan <pg@bowt.ie>
Reviewed-By: Michael Paquiër <michael@paquier.xyz>
Discussion: https://postgr.es/m/CAH2-WznJt9CMM9KJTMjJh_zbL5hD9oX44qdJ4aqZtjFi-zA3Tg@mail.gmail.com
Backpatch: 10-

src/include/libpq/hba.h

@@ -169,7 +169,7 @@ extern const char *hba_authname(UserAuth auth_method);
 extern void hba_getauthmethod(hbaPort *port);
 extern int	check_usermap(const char *usermap_name,
 						  const char *pg_role, const char *auth_user,
-						  bool case_sensitive);
+						  bool case_insensitive);
 extern HbaLine *parse_hba_line(TokenizedAuthLine *tok_line, int elevel);
 extern IdentLine *parse_ident_line(TokenizedAuthLine *tok_line, int elevel);
 extern bool pg_isblank(const char c);