Revert "expression: fix wrong result type for greatest/least (#29408)"

[guo-shaoge]

Reverts #29912

MySQL and tidb before this pr:

mysql> select greatest(time '20:00:00', 120000);
+-----------------------------------+
| greatest(time '20:00:00', 120000) |
+-----------------------------------+
| 20:00:00                          |
+-----------------------------------+
1 row in set (3.25 sec)

tidb after this pr:

mysql>  select greatest(time '20:00:00', 120000);
+-----------------------------------+
| greatest(time '20:00:00', 120000) |
+-----------------------------------+
| 2020-00-00 00:00:00               |
+-----------------------------------+
1 row in set (0.00 sec)

Release note

None

[ti-chi-bot]

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• XuHuaiyu
• wshwsh12

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[XuHuaiyu]

LGTM

[wshwsh12]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 3901282

[guo-shaoge]

/run-check_dev

[XuHuaiyu]

/merge

[zhouqiang-cl]

/merge

[XuHuaiyu]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 9db6123