Removed auth_cfg_t.replace_value() and replaced usages with add().

replace_value() was used to replace identities. Since for these the latest is
now returned by get(), adding the new identity with add() is sufficient.

src/libstrongswan/credentials/auth_cfg.h

@@ -196,15 +196,6 @@ struct auth_cfg_t {
 	void (*replace)(auth_cfg_t *this, enumerator_t *pos,
 					auth_rule_t rule, ...);
 
-	/**
-	 * Replace the value of the first rule with the given type.
-	 *
-	 * @param rule		rule type
-	 * @param ...		associated value to rule
-	 * @return			TRUE if the rule was found and the value replaced
-	 */
-	bool (*replace_value)(auth_cfg_t *this, auth_rule_t rule, ...);
-
 	/**
 	 * Check if a used config fulfills a set of configured constraints.
 	 *