revert frontend part of "fix broken iframe vomnibar if an extension page is disabled"
revert frontend part of "fix broken iframe vomnibar if an extension page is disabled"

According to documents, `iframe:window:postMessage` won't throw directly,
so the code can not work.

I haven't found any method to catch / get to know the error. Waiting for
further investigation.

gdh1995/vimium-plus,gdh1995/vimium-plus,gdh1995/vimium-plus