Remove the test for `webgpu.force-enabled` from the MIDI
`crashtests.list` file. I'm not sure what this pref is doing in this
giant list, or indeed what this giant list is doing at all, but that
pref doesn't exist any more, so it can't hurt to remove it.
Depends on D190203
Differential Revision: https://phabricator.services.mozilla.com/D190204