Kick bundlesize out of package.json

This pulled in ancient versions of brotli-size (unlikely to be fixed:
siddharthkp/bundlesize#370 (comment))
which broke CI on Node 20. IIUC, it shouldn’t even be needed anymore now
that bundle size can be tested via BundleSizeTestBase instead; but in
any case this can be figured out later, *after* CI is restored for the
many extensions that pull in Popups.

Bug: T382192
Bug: T360590
Change-Id: I86413a7707cbd33fd473f8a1daf6c7866fbb473f
(cherry picked from commit 300e32b)