Here in ๐, Oliver Cowdery wrote poverty as poverity. Although normally Oliver wrote the word correctly (five times in ๐ and six times in ๐), he occasionally miswrote it (but only in ๐) as a word ending in -ity, here in Helaman 13:31 and two times earlier in the text:
For these other two instances, ๐ is extant and correctly reads as poverty. Thus Oliver is the one responsible for poverity; it does not represent some kind of archaic or dialectal form for the word poverty (nor is this form of the word found in the Oxford English Dictionary).
Summary: Maintain the word poverty throughout the text; in a few places, Oliver Cowdery wrote the word as poverity in ๐, but that form of the word is clearly innovative and not original to the Book of Mormon text.