Wesnoth: Use of $unit.overlays in ANL, DiD and SotA

[stevecotton]

As of PR #4211, setting [unit]overlays= works, but the [unit]overlays attribute will always be empty if WML tries to read it. This means the following three uses are now broken:

• [x] SotA's lichify macro overlays=$stored_necromancer.overlays
• [x] DiD's copy of that lichify macro (@nemaara, is this going to be removed anyway?)
• [x] ANL's clearing of critter's overlays:
  https://github.com/wesnoth/wesnoth/blob/a075a2971c192aec381fa31311953fef4c11a456/data/multiplayer/scenarios/ANL_utils/ANL_special_macros.cfg#L218-L220

[nemaara]

I already removed that here https://github.com/wesnoth/wesnoth/commit/79d97a11898d15c314b1f8cb7b127c473898bc33.

[stevecotton]

Removed the leftover DiD code in 80b03f1a05e86bfe794a4482b4ab2ce23ae6b219

[sevu]

Will change the ANL code

[sigurdfdragon]

Removed from SotA in f55704cff8753bb771e06d2fce6286dddc825883

[sevu]

5ee5920 changes the ANL part.