[Qt] plugin is loaded to the web process via MainResourceLoader::substituteMIMETypeFr...

[Qt] plugin is loaded to the web process via MainResourceLoader::substituteMIMETypeFromPluginDatabase
https://bugs.webkit.org/show_bug.cgi?id=86489

Reviewed by Simon Hausmann.

Removed the substituteMIMETypeFromPluginDatabase quirk from
MainResourceLoader. It would be possible to fix it in a way
that is compatible with WebKit2, but given that it was a Qt
only fix, and that it's not clear that we still need it, and
it's not even work currently, I decided to remove it. At least
it is -1 platform ifdef in common code.

Just removed a non-tested quirk, no test needed.

* loader/MainResourceLoader.cpp:
(WebCore::MainResourceLoader::didReceiveResponse):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@121423 268f45cc-cd09-0410-ab3c-d52691b4dbfc