C++: remove unused function

gotoslot_test.cpp:70:9: warning: unused function 'expectedContentsForFile' [-Wunused-function]
QString expectedContentsForFile(const QString &filePath)
        ^

Change-Id: Ibc9d540e241cd90365235ee75de213fcda107e32
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@digia.com>