test: Reject all FF+Windows ClearKey testing (#8122)

My previous change, #8109, didn't go far enough. In a full test run,
some ClearKey tests still crash Firefox in the lab. By removing it from
the support dictionary used to gate DRM tests, we ensure all ClearKey
tests are skipped.

Author: joeyparrish

lib/media/drm_engine.js

@@ -1823,7 +1823,8 @@ shaka.media.DrmEngine = class {
         if (goog.DEBUG &&  // not a production build
             shaka.util.Platform.isWindows() &&  // on Windows
             shaka.util.Platform.isFirefox()) {  // with Firefox
-          // Do nothing, to avoid a crash in the FF ClearKey CDM.
+          // Reject this, since it crashes our tests.
+          throw new Error('Suppressing Firefox Windows ClearKey in testing!');
         } else {
           // Otherwise, create the CDM.
           await access.createMediaKeys();