random: drop ad-hoc Shuffle in favor of std::shuffle

Benchmarks show it is no longer faster with modern standard C++ libraries,
and the debug-mode failure due to self-move has been fixed as well.

src/random.h

@@ -458,29 +458,6 @@ inline uint256 GetRandHash() noexcept
     return hash;
 }
 
-/** More efficient than using std::shuffle on a FastRandomContext.
- *
- * This is more efficient as std::shuffle will consume entropy in groups of
- * 64 bits at the time and throw away most.
- *
- * This also works around a bug in libstdc++ std::shuffle that may cause
- * type::operator=(type&&) to be invoked on itself, which the library's
- * debug mode detects and panics on. This is a known issue, see
- * https://stackoverflow.com/questions/22915325/avoiding-self-assignment-in-stdshuffle
- */
-template <typename I, RandomNumberGenerator R>
-void Shuffle(I first, I last, R&& rng)
-{
-    while (first != last) {
-        size_t j = rng.randrange(last - first);
-        if (j) {
-            using std::swap;
-            swap(*first, *(first + j));
-        }
-        ++first;
-    }
-}
-
 /* ============================= MISCELLANEOUS TEST-ONLY FUNCTIONS ============================= */
 
 /** Check that OS randomness is available and returning the requested number