Bug 1885101: Match screen and window properties with top window for...

Bug 1885101: Match screen and window properties with top window for ScreenRect, ScreenAvailRect and WindowOuterSize. r=timhuang,emilio

This patch removes test_iframe.html. We remove it because the newly introduced test covers the tests done in that test. The reason for removing it in the first place is now that screen properties are inherited/spoofed xorigin, we get a 4px difference. The reasosn for 4px difference is the test runner runs tests in an iframe with a 2px border on each side.

Differential Revision: https://phabricator.services.mozilla.com/D215509