Fix AuraManager OOS on rejoin following rP20737 / D1108.

The AuraManager serialized the affects array of the aura JSON files, while the Auras components create new affects arrays upon deserialization.
So the AuraManager of rejoined clients failed to identify and remove the according aura effects of units who received the aura effect before the rejoin.

Fix it by not serializing the array but only the strings inside the array.
It were preferable to rebuild the modification cache and remove the serialization altogether, refs #3834.

rP18100 introduced the same OOS on rejoin, refs #3909, #4239, but it wasn't noticed due to the revert in rP18804.

Differential Revision: https://code.wildfiregames.com/D1201
Reviewed By: bb
Comments By: gameboy
Fixes #4924