It appears that the word which originally had an L in its spelling as well as pronunciation. But its modern pronunciation doesn't have an L.
Wikitionary has:
From Middle English which, hwic, wilche, hwilch, whilk, hwilc, from Old English hwelċ (“which”)
One of its Middle English form hwilc's pronunciation is /xwilt͡ʃ/ ([ʍiɫt͡ʃ]).
Its Old English hwelc's pronunciation is /xwelt͡ʃ/ ([ʍeɫt͡ʃ])
[Transcriptions from Wikitionary]
Etymology Dictionary also agrees on hwilc but doesn't explain the loss of the L.
This Google book shows some uses of "hwilc" and also records the spelling hwylc
The change from hw to wh is answered in this question (John Lawler's answer seems reasonable), but I didn't find any related question about the loss of the L. I also didn't find any other source for it.
Why did it lose the L? Is there a good reason for it or is it a random loss?