Vorpal technique no longer added to weapons

### Describe the bug

When killing a Jabberwock with an appropriate diamond weapon, the vorpal technique is not added to its list of available techniques.

### Steps To Reproduce

1. Obtain a diamond weapon (tried with zweihander, nodachi, katana)
2. Spawn a jabberwock
3. Kill the jabberwock using the weapon
4. Check technique list

### Expected behavior

For the Vorpal technique to appear in the item's technique list, as it has previously.

### Screenshots

_No response_

### Versions and configuration

- OS: Windows
- OS Version: 10.0 2009
- Game Version: 5eb505a [64-bit]
- Graphics Version: Tiles
- Game Language: System language []
- Mods loaded: [
Dark Days Ahead [dda],
Disable NPC Needs [no_npc_food],
Bionic Professions [package_bionic_professions],
Aftershock [aftershock],
Blaze Industries [blazeindustries],
Magiclysm [magiclysm],
DinoMod [DinoMod],
My Sweet Cataclysm [my_sweet_cataclysm],
Mythical Martial Arts [MMA],
SpeedyDex [speedydex],
Stats Through Skills [StatsThroughSkills]
]

### Additional context

Looking at the mondeath.cpp file, this appears to have been an issue with #49439 where the vorpal functionality was removed from the file but not readded anywhere else.

Start by inspecting mondeath.cpp and the changes from issue #49439, which the report identifies as removing the vorpal functionality. Reproduce the Jabberwock kill with a diamond weapon and check the weapon's technique list. Done means the Vorpal technique appears again after the appropriate kill.

Written by the indexing model from the issue text.