tst_QProcess: Remove macro QPROCESS_VERIFY().

It was used to verify waitForFinished() and printed QProcess::errorString()
on failure, which is misleading, since the process is not
in an error state - it is still running. Example:

QWARN  : tst_QProcess::setStandardOutputFileAndWaitForBytesWritten() QProcess error: 5: Unknown error
FAIL!  : tst_QProcess::setStandardOutputFileAndWaitForBytesWritten() 'ret' returned FALSE. ()

Use a plain QVERIFY instead.

Task-number: QTBUG-47370
Change-Id: Iacfa6e1a5ffd2be4e1257a27a400ccc59671e8c8
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@theqtcompany.com>