shape-outside, shape-margin, shape-image-threshold have been shipped in Firefox
62. We can remove the preference.

The change in devtools/shared/css/generated/properties-db.js is generated by
"./mach devtools-css-db"

The actual shape-image CORS mode tests in file_shape_outside_CORS.html are
moved into test_shape_outside_CORS.html because we don't need the <iframe>
trick to enable the feature.

Differential Revision: https://phabricator.services.mozilla.com/D10804