test: remove reference to whatwg in file names under test/wpt

WPT covers standards in both W3C and WHATWG, as such it would be
strange to make this disparity explicit in our file names
(e.g. when testing standards that are solely in W3C, like
performance-timeline). Remove the reference to WHATWG will
also make the file names shorter.

PR-URL: https://github.com/nodejs/node/pull/24826
Refs: https://github.com/nodejs/node/issues/24823


Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>