bytecode: Do not generate `SLIDE x 0` instructions

SLIDE x 0 is a no-op as it means to shift x elements of the stack by no
spaces. In the interpreter, this results in a loop which copies an array
element into the same place.

I have instrumented GHCi to count how many of these instructions are interpreted.
The workload was `ghc` compiling two simple modules.

Total no-op slides: 7793476
Total slides: 11413289
Percentage useless (slides): 68%
Percentage uselss of total instructions: 9%