[CI] Let ParallelTestRunner determine the appropriate number of workers (#734)

Author: christiangnrd

test/runtests.jl

@@ -1,15 +1,6 @@
 using Metal
 using ParallelTestRunner
 
-# Force 3 workers if running on the 8GB buildkite mac minis
-#  until ParallelTestRunner.jl interface to determine # workers
-if parse(Bool, get(ENV, "BUILDKITE", "false"))
-    jobs_pos = findfirst(arg -> startswith(arg, "--jobs"), ARGS)
-    if isnothing(jobs_pos) && (Sys.total_memory() == 8*2^30)
-        push!(ARGS, "--jobs=3")
-    end
-end
-
 # Quit without erroring if Metal loaded without issues on unsupported platforms
 if !Sys.isapple()
     @warn """Metal.jl succesfully loaded on non-macOS system.