[TBC bracket] Disable Level 70 "Artisan Riding" mail

Refernced to: https://github.com/chromiecraft/chromiecraft/issues/6533

Same as: https://github.com/azerothcore/mod-progression-system/commit/db6a5ed1e4169127e4c471bc5b6f21a50c91d66f

## Horde

mail_level_reward
---
| level | raceMask | mailTemplateId | senderEntry |
| ---: | ---: | ---: | ---: |
| 70 | 690 | 285 | 35135 |

```
From: Wind Rider Sabamba
Subject: Artisan Riding at Warsong Hold

How you doing, Hordembe.

If you want to learn Artisan Riding for faster flying mounts, visit me at Warsong Hold in Borean Tundra. My fee is five thousand gold coins, plus a thousand for more Cold Weather Flying training if you want to ride in Northrend.

If you want a swift flying mount once you learn, Tohfo Skyhoof sells them for no more than one hundred gold coins.

- Sabamba

P.S. If you can't make it to Northrend, visit Wind Rider Jahubo at Thrallmar in Hellfire Peninsula.
```

## Alliance

mail_level_reward
---
| level | raceMask | mailTemplateId | senderEntry |
| ---: | ---: | ---: | ---: |
| 70 | 1101 | 284 | 35133 |

```
From: Maigra Keenfeather
Subject: Artisan Riding at Valiance Keep

Hey there, lad! Looking to learn Artisan Riding for faster flying mounts? Then visit me at Valiance Keep in Borean Tundra.

My fee's five thousand gold coins, plus a thousand for more Cold Weather Flying training if you want to ride in Northrend.

If you want a swift flying mount, the good Durgan Thunderbeak offers them for no more than one hundred gold coins a piece.

- Maigra

P.S. If you can't make it to Northrend, visit Hargen Bronzewing at Honor Hold in Hellfire Peninsula.
```

Start by reviewing the referenced ChromieCraft issue and AzerothCore commit, then locate the mail_level_reward data for level 70 and the listed Horde and Alliance entries. Done means those Artisan Riding mails are no longer awarded while other level rewards remain unchanged; verify with the repository's available database or progression tests.

Written by the indexing model from the issue text.