[Qt][Mac] Remove obsolete workaround for debug builds
https://bugs.webkit.org/show_bug.cgi?id=114750

Reviewed by Jocelyn Turcotte.

This workaround made default builds fail with recent Qt5 because
it removed the major version number from the library name, producing
QtWebKitWidgets, whereas the linking command line tried to link
against Qt5WebKitWidgets.
Debug builds are possible with and without framework-enabled builds
of Qt, but the debug versions of the Qt libraries have to be present.
Debug builds with a release version of Qt are not possible on Mac
since for debug builds qmake produces a linker command line where
all the Qt libraries have the "_debug" suffix, therefore if the debug
libraries are missing the build fails.

* Source/widgetsapi.pri:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@148789 268f45cc-cd09-0410-ab3c-d52691b4dbfc