mysql_client: convert old-style hook to new-style hook

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/mysql_client/mysql_client.mk

@@ -32,8 +32,10 @@ MYSQL_CLIENT_CONF_OPT = \
 	--enable-thread-safe-client \
 	$(ENABLE_DEBUG)
 
-$(eval $(call AUTOTARGETS,package,mysql_client))
-
-$(MYSQL_CLIENT_HOOK_POST_INSTALL):
+define MYSQL_CLIENT_REMOVE_TEST_PROGS
 	rm -rf $(TARGET_DIR)/usr/mysql-test $(TARGET_DIR)/usr/sql-bench
-	touch $@
+endef
+
+MYSQL_CLIENT_POST_INSTALL_TARGET_HOOKS += MYSQL_CLIENT_REMOVE_TEST_PROGS
+
+$(eval $(call AUTOTARGETS,package,mysql_client))