`/kill @e[type=Slime]` will kill all the Slimes in the world while leaving everything else alone. With this command in a Command Block, an automatic elimination of Slimes is possible: Just set it to Repeat and Always Active, and then you're done.

[How can I get a Command Block?][1]


  [1]: https://gaming.stackexchange.com/questions/236324/how-can-i-get-a-command-block