Check all foreign key constraints without `ON DELETE` clause

[eldering]

Description of the problem

In #2464 it was found that we have a foreign key constraint that should have an ON DELETE CASCADE clause. In general, almost every FK constraint should have either ON DELETE CASCADE or ON DELETE SET NULL. We should check and if necessary fix all of these:

CREATE TABLE `debug_package`
  CONSTRAINT `FK_9E17399BE0E4FC3E` FOREIGN KEY (`judgehostid`) REFERENCES `judgehost` (`judgehostid`)

-- This one is ok I think:
CREATE TABLE `executable`
  CONSTRAINT `FK_D68EDA01979A9F09` FOREIGN KEY (`immutable_execid`) REFERENCES `immutable_executable` (`immutable_execid`)

CREATE TABLE `judgetask`
  CONSTRAINT `judgetask_ibfk_1` FOREIGN KEY (`judgehostid`) REFERENCES `judgehost` (`judgehostid`)

CREATE TABLE `judging_run`
  CONSTRAINT `judging_run_ibfk_1` FOREIGN KEY (`testcaseid`) REFERENCES `testcase` (`testcaseid`),

CREATE TABLE `version`
  CONSTRAINT `FK_BF1CD3C32271845` FOREIGN KEY (`langid`) REFERENCES `language` (`langid`),
  CONSTRAINT `FK_BF1CD3C3E0E4FC3E` FOREIGN KEY (`judgehostid`) REFERENCES `judgehost` (`judgehostid`)

[tuupke]

Fixed in #2658.