The dead lion is not surrounded by flies but bees. Here's the information from the Lyle's Golden Syrup Website:
In 1904, the “lion and bees” tin was registered as Lyle’s trademark. The design comes from Abram Lyle’s religious beliefs: It’s a reference to a story in the Old Testament, in which Samson killed a lion, then saw that bees had formed a honeycomb in the lion’s carcass. The Bible references Samson’s words that also feature on the tin, “Out of the strong came forth sweetness.” The logo and design remain unchanged today.
Yes, It's a strange logo, but at least it has some meaning according to the company.