doc: remove superfluous sample assert code

Remove superfluous sample code. Since `assert()` is documented as an
alias of `assert.ok()` and nothing more, the sample code for
`assert.ok()` is sufficient.

PR-URL: https://github.com/nodejs/node/pull/11933
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

doc/api/assert.md

@@ -12,22 +12,7 @@ added: v0.5.9
 * `value` {any}
 * `message` {any}
 
-An alias of [`assert.ok()`][] .
-
-```js
-const assert = require('assert');
-
-assert(true);
-// OK
-assert(1);
-// OK
-assert(false);
-// throws "AssertionError: false == true"
-assert(0);
-// throws "AssertionError: 0 == true"
-assert(false, 'it\'s false');
-// throws "AssertionError: it's false"
-```
+An alias of [`assert.ok()`][].
 
 ## assert.deepEqual(actual, expected[, message])
 <!-- YAML