Bug 1666830 [wpt PR 25717] - Fix tests that return values to async_test in encrypted-media/, a=testonly

Automatic update from web-platform-tests
Fix tests that return values to async_test in encrypted-media/ (#25717)

In both cases here, the test was correctly written for async_test, they
just didn't need to return the promise they used as part of the test
flow.

See https://github.com/web-platform-tests/wpt/issues/21435
--

wpt-commits: d0804458e8797790f61efc73ab2446c6e507a30f
wpt-pr: 25717

testing/web-platform/tests/encrypted-media/scripts/onencrypted.js

@@ -25,7 +25,7 @@ function runTest(config) {
             };
 
         waitForEventAndRunStep('encrypted', video, onEncrypted, test);
-        return testmediasource(config).then(function (source) {
+        testmediasource(config).then(function (source) {
             mediaSource = source;
             config.video.src = URL.createObjectURL(mediaSource);
             return source.done;

testing/web-platform/tests/encrypted-media/scripts/reset-src-after-setmediakeys.js

@@ -39,7 +39,7 @@ function runTest(config)
         };
 
         // Create a MediaKeys object and assign it to video.
-        return navigator.requestMediaKeySystemAccess(keysystem, [configuration]).then(test.step_func(function (access) {
+        navigator.requestMediaKeySystemAccess(keysystem, [configuration]).then(test.step_func(function (access) {
             assert_equals(access.keySystem, keysystem);
             return access.createMediaKeys();
         })).then(test.step_func(function (result) {