[lacros] Re-enable TwoSubframesCreatePopupMenuWidgetsSimultaneously test

The flakiness was introduced by this CL https://crrev.com/c/2397715
which was a reland of CL that was reverted because it made this test flaky.

Bug: 1111979
Change-Id: I3153d0a27a85f36b282406f3cf15c6661d060dac
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2402160Reviewed-by: Giovanni Ortuño Urquidi <ortuno@chromium.org>
Commit-Queue: Sven Zheng <svenzheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#805599}

testing/buildbot/filters/lacros.content_browsertests.filter

@@ -3,6 +3,5 @@
 -OutOfProcessPPAPITest.TrueTypeFont
 
 # Following tests are flaky.
--All/SitePerProcessBrowserTest.TwoSubframesCreatePopupMenuWidgetsSimultaneously*
 -All/WebContentsVideoCaptureDeviceBrowserTestP.CapturesContentChanges*
 -PDFExtensionTestWithTestGuestViewManager*
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