Revert "Problem 14, Longest Collatz sequence"

This reverts commit 1e6de07c553bbad4528d0a9ea19dce58f2d5ae03.
Problem 1

If we list all the natural numbers below 10 that are multiples of 3 or
5, we get 3, 5, 6 and 9. The sum of these multiples is 23.

Find the sum of all the multiples of 3 or 5 below 1000.