Remove unused make variable from DerivedSources.make
https://bugs.webkit.org/show_bug.cgi?id=110306

Patch by Laszlo Gombos <l.gombos@samsung.com> on 2013-02-22
Reviewed by Alexey Proskuryakov.

r107026 removed the last piece of logic that was guarded with
ENABLE_DASHBOARD_SUPPORT, so now it can be removed from
DerivedSources.make.

Also combined the way ENABLE_ORIENTATION_EVENTS is set to 0
to make it more readable.

No new tests, no new functionality.

* DerivedSources.make:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@143820 268f45cc-cd09-0410-ab3c-d52691b4dbfc