asynctypes-685526: s/assert.skip/assert.log/g

Having a separate function to declare skipped tests made some sense when
we had a custom UI for displaying test results, but we didn't make
anything of it, and we don't control the test results ui in firefox so
replace assert.skip with assert.log.

Signed-off-by: Joe Walker <jwalker@mozilla.com>
asynctypes-685526: Extra skips for Firefox

Firefox has a tilt command which we shouldn't unregister, which clashes
with some of our hint tests, and the skip clause in testKeyboard was
always wrong but masked by a jsdom skip rule.

Signed-off-by: Joe Walker <jwalker@mozilla.com>