test: move simple/test-crypto-dh to pummel/

The test is too slow / CPU intensive for the main test harness.

diff --git a/test/simple/test-crypto-dh.js b/test/pummel/test-crypto-dh.js
similarity index 100%
rename from test/simple/test-crypto-dh.js
rename to test/pummel/test-crypto-dh.js