tools: enable eslint no-undef-init rule

This also fixes the three entries that did not pass.

Backport-PR-URL: #19244
PR-URL: #18831
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Matheus Marchini <matheus@sthima.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

test/parallel/test-fs-utimes.js

@@ -88,7 +88,7 @@ function testIt(atime, mtime, callback) {
       expect_errno('futimesSync', fd, ex, 'ENOSYS');
     }
 
-    let err = undefined;
+    let err;
     try {
       fs.utimesSync('foobarbaz', atime, mtime);
     } catch (ex) {