Bug 1781936 - Propagate GeckoView settings on BrowsingContext replacement. r=nika

This should be a better fix. GeckoView assumes these don't change on .top
unless they are explicitly set.

I don't have an Android build environment handy, but I'll try to confirm.

Also, remove an unused flag while at it.

Differential Revision: https://phabricator.services.mozilla.com/D153107

docshell/base/nsDocShell.cpp

@@ -390,7 +390,6 @@ nsDocShell::nsDocShell(BrowsingContext* aBrowsingContext,
       mTitleValidForCurrentURI(false),
       mWillChangeProcess(false),
       mIsNavigating(false),
-      mSuspendMediaWhenInactive(false),
       mForcedAutodetection(false),
       mCheckingSessionHistory(false),
       mNeedToReportActiveAfterLoadingBecomesActive(false) {