'listen' has some code in it to try to not re-set a map for an existing mapping, by checking the 'desc' of the table returned from 'get_map'. Since 'desc' was never included in the table returned from 'get_map', I'm assuming my changes here were always the intention.
This change seems to fix an issue I was seeing (with cmp-nvim-ultisnips at least) where every time I'd enter and leave Insert mode, seemingly another <Tab> handler was getting registered, overtime causing <Tab> in Insert mode to get slower and slower.
c49ad26e89