Fix remaining functional test failures and compatibility with firefox 68

Fix remaining functional test failures and drop a few more code that become unused now that we have a setFile command.

Because firefox 68 executes event handlers for events triggered on disabled elements ( https://phabricator.services.mozilla.com/D10000 ), Zelenium is also adapted to mimic the behaviour we had with firefox 52 (and chrome behavior) of not executing event hander.

TODO:

• testContributeTab sometimes displays Converted, sometimes Converting. I wonder if we can wait for something to make the test deterministic, otherwise we can assert a regexp.
• erp5_web_renderjs_ui_test:testFunctionalRJSCore ( discussed in https://lab.nexedi.com/nexedi/erp5/commit/05b9c4afa2bdf9a2f1b76ac94e70859bdea7e8b5#note_87278 )
• someone update test nodes to use new firefox.
• understand why with firefox 58 selenium sends clicks on disabled button.