Simplify realtime method

We probably aren't running these benchmarks on rubies
that don't have these methods.
If we are, they probably don't have their own alternate implementation
of Benchmark.realtime.
If we need to support something else we should just add a version that
uses Time.now.to_f.

Author: rwstauner

harness/harness.rb

@@ -18,18 +18,10 @@
 
 puts RUBY_DESCRIPTION
 
-if defined?(Process.clock_gettime) && defined?(Process::CLOCK_MONOTONIC)
-  def realtime
-    r0 = Process.clock_gettime(Process::CLOCK_MONOTONIC)
-    yield
-    Process.clock_gettime(Process::CLOCK_MONOTONIC) - r0
-  end
-else
-  require "benchmark"
-
-  def realtime(&block)
-    Benchmark.realtime(&block)
-  end
+def realtime
+  r0 = Process.clock_gettime(Process::CLOCK_MONOTONIC)
+  yield
+  Process.clock_gettime(Process::CLOCK_MONOTONIC) - r0
 end
 
 # Takes a block as input