Layout Test plugins/embed-attributes-setting.html is flaky.

[Matt Lewis]

plugins/embed-attributes-setting.html is a flaky failure on macOS Sierra WK2 Release according to the dashboard:

https://webkit-test-results.webkit.org/dashboards/flakiness_dashboard.html#showAllRuns=true&tests=plugins%2Fembed-attributes-setting.html

This doesn't seem to have recently started based on the dashboard.

First failure on board:
https://build.webkit.org/results/Apple%20Sierra%20Release%20WK2%20(Tests)/r221805%20(4175)/results.html
https://build.webkit.org/builders/Apple%20Sierra%20Release%20WK2%20(Tests)/builds/4175

Current build:
https://build.webkit.org/results/Apple%20Sierra%20Release%20WK2%20(Tests)/r222556%20(4579)/results.html
https://build.webkit.org/builders/Apple%20Sierra%20Release%20WK2%20(Tests)/builds/4579

Diff:

--- /Volumes/Data/slave/sierra-release-tests-wk2/build/layout-test-results/plugins/embed-attributes-setting-expected.txt
+++ /Volumes/Data/slave/sierra-release-tests-wk2/build/layout-test-results/plugins/embed-attributes-setting-actual.txt
@@ -5,11 +5,11 @@
 PASS: embed.getAttribute('width') should be 1 and is.
 PASS: embed.getAttribute('type') should be 1 and is.
 PASS: embed.getAttribute('src') should be 1 and is.
-PASS: typeof embed.testCallback should be function and is.
+FAIL: typeof embed.testCallback should be function but instead is undefined.
 ----------
 [Embed is dynamically created element with only type specified]
-PASS: typeof embed.testCallback should be function and is.
+FAIL: typeof embed.testCallback should be function but instead is undefined.
 ----------
 [Embed is dynamically created element with only src specified]
-PASS: typeof embed.testCallback should be function and is.
+FAIL: typeof embed.testCallback should be function but instead is undefined.

[Alexey Proskuryakov]

Mass closing plug-in bugs, as plug-in support has been removed from WebKit.

Please comment and/or reopen if this still affects WebKit in some way.