test: merge test-crypto-dh-hash with modp18 test

This test file was split because it was taking a long time in some
versions of OpenSSL 1.1.1, but that is not the case anymore with
OpenSSL 3.0, so merge the tests again.

Refs: nodejs#34631

Author: tniessen

test/pummel/test-crypto-dh-hash-modp18.js

@@ -41,6 +41,7 @@ const hashes = {
   modp15: '7bdd39e5cdbb9748113933e5c2623b559c534e74',
   modp16: 'daea5277a7ad0116e734a8e0d2f297ef759d1161',
   modp17: '3b62aaf0142c2720f0bf26a9589b0432c00eadc1',
+  modp18: 'a870b491bbbec9b131ae9878d07449d32e54f160',
 };
 
 for (const name in hashes) {