Remove SRCDIR defines from tests that don't use them. There is a
standard define called QT_TESTCASE_SOURCEDIR that is available to all
tests and serves the same purpose.
Pick-to: 6.2
Change-Id: I2aa237739c011495e31641cca525dc0eeef3c870
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>