Care to elaborate on that "quadratic" comment?

Say you want to delete all elements in the second half of the array. The first N/2 iterations of your loop, no splicing happens. But on the N/2 + 1^st iteration, the splicing takes at least N/2 - 1 steps, as that many array elements need to be moved. On the N/2 + 2^nd iteration, the splicing takes at least N/2 - 2 steps. In total, you will be moving

Σ^N/2-1_i=1(i)

array elements. If I've done my math correctly, the above sum equals (N² - 2N + 4)/8. Which means your algorithm runs in Ω(N²) time.