Omit redundant computation

This stems from an earlier mistake where I was using primes in the first
wheel, rather than coprimes-to-the-basis.  1 is not prime, so we used to
need to handle it separately (in an implementation which was, to be
clear, wrong).  It _is_ coprime, so now we get it for free!

src/core/include/units/bits/prime.h

@@ -149,10 +149,6 @@ struct wheel_factorizer {
     }
 
     for (std::size_t wheel = wheel_size; wheel < n; wheel += wheel_size) {
-      if (const auto k = first_factor_maybe(n, wheel + 1)) {
-        return *k;
-      }
-
       for (const auto& p : coprimes_in_first_wheel) {
         if (const auto k = first_factor_maybe(n, wheel + p)) {
           return *k;