[Qt][TestWebKitAPI] The activeBuildConfig() function has been replaced with targetSubDir()

Rubber-stamped by Csaba Osztrogonác.

Besides suppressing a warning about the non-existing function this
fixes the build if there is a subdirectory (eg. debug-and-release).

* TestWebKitAPI/InjectedBundle.pri:
* TestWebKitAPI/TestWebKitAPI.pri:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@144299 268f45cc-cd09-0410-ab3c-d52691b4dbfc