test: remove string literal from strictEqual

Remove obsolete string literals from `assert.strictEqual()` calls in
test/parallel/test-stream-pip-await-drain-push-while-write.js.

PR-URL: #20920
Refs: https://www.nodetodo.org/getting-started
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

test/parallel/test-stream-pipe-await-drain-push-while-write.js

@@ -7,17 +7,15 @@ const writable = new stream.Writable({
   write: common.mustCall(function(chunk, encoding, cb) {
     assert.strictEqual(
       readable._readableState.awaitDrain,
-      0,
-      'State variable awaitDrain is not correct.'
+      0
     );
 
     if (chunk.length === 32 * 1024) { // first chunk
       readable.push(Buffer.alloc(34 * 1024)); // above hwm
       // We should check if awaitDrain counter is increased in the next
       // tick, because awaitDrain is incremented after this method finished
       process.nextTick(() => {
-        assert.strictEqual(readable._readableState.awaitDrain, 1,
-                           'Counter is not increased for awaitDrain');
+        assert.strictEqual(readable._readableState.awaitDrain, 1);
       });
     }