Bug 254403

Currently we have a multitude of pretty similar baseline search paths, and it's often unclear where expectations should go.

As an attempt to simplify this, I suggest:

* The default baseline always corresponds to wk2 (this avoids a necessity to have, e.g., "mac", "mac-wk1", "and "mac-wk2": it becomes clear the wk2 expectation belongs in "mac"). This also implies getting rid of "wk2" as a place with expectations, and potentially adding a "wk1" (though do any ports aside from Apple still maintain WK1 and thus test expectations?).

* We move to only having "ios" (and not also "ios-simulator", "ios-device"), as this split is meaningless in WebKit where nobody outside of Apple can run tests on non-Simulator iOS and hence the expectations need to be maintained by Apple anyway. (And, e.g., if someone puts a failing expectation in ios-simulator in WebKit then we can quite easily end up with duplicate expectations between ios-simulator and ios-device, which helps nobody.) Note jbedard did related work in 187099@main.