test: remove superfluous check in pummel/test-timers

If setTimeout is not a function, this test and most other tests would
fail. There is no need to check it.

PR-URL: #34488
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Pranshu Srivastava <rexagod@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>

test/pummel/test-timers.js

@@ -27,7 +27,6 @@ const WINDOW = 200; // Why does this need to be so big?
 
 let interval_count = 0;
 
-assert.strictEqual(setTimeout instanceof Function, true);
 const starttime = new Date();
 setTimeout(common.mustCall(function() {
   const endtime = new Date();